Recent Progress in Nanoparticles Based Sensors for the Detection of Mercury (II) Ions in Environmental and Biological Samples

To maintain a green and sustainable environment for human beings, rapid detection of potentially toxic heavy metals like mercury (Hg(II)) has attracted great attention. Recently, sensors have been designed which can selectively detect Hg(II) over other common available cations and give a naked eye or fluorometric response. In the last two decades, the trend is shifting from bulky organic chemosensors toward nanoparticles due to their rapid response, low cost, eco-friendly and easy synthesis. In this review, promising nanoparticles-based sensors for Hg(II) detection are discussed. The nano-sensors are functionalized with nucleotide or other suitable materials which coordinate with Hg(II) ions and give clear color or fluorescence change. The operational mechanisms are discussed focusing on its four basic types. The nanoparticles-based sensors are even able to detect Hg in three different oxidation states (Hg(II), Hg(I) and Hg(0)). Recently, the trend has been shifted from ordinary nanoparticles to magnetic nanoparticles to simultaneously detect and remove Hg(II) ions from environmental samples. Furthermore, the nano-sensors for Hg(II) are compared with each other and with the reported organic chemosensors.

Antimicrobial macrozones interact with biological macromolecules via two-site binding mode of action: Fluorimetric, NMR and docking studies

Macrozones are novel conjugates of azithromycin and thiosemicarbazones, which exhibit very good in vitro antibacterial activities against susceptible and some resistant bacterial strains thus showing a potential for further development. A combination of spectrometric (fluorimetry, STD and WaterLOGSY NMR) and molecular docking studies provided insights into atomic details of interactions between selected macrozones and biological receptors such as E. coli ribosome and bovine serum albumin. Fluorimetric measurements revealed binding constants in the micro-molar range while NMR experiments provided data on binding epitopes. It has been demonstrated that both STD and WaterLOGSY gave comparable and consistent results unveiling atoms in intimate contacts with biological receptors. Docking studies pointed towards main interactions between macrozones and E. coli ribosome which included specific π - π stacking and hydrogen bonding interactions with thiosemicarbazone part extending down the ribosome exit tunnel. The results of the docking experiments were in fine correlation with those obtained by NMR and fluorimetry. Our investigation pointed towards a two-site binding mechanism of interactions between macrozones and E. coli ribosome which is the most probable reason for their activity against azithromycin-resistant strains. Much better activity of macrozone-nickel coordinated compound against E. coli ribosome compared to other macrozones has been attributed to the higher polarity which enabled better bacterial membrane penetration and binding of the two thiosemicarbazone units thus additionally contributing to the overall binding energy. The knowledge gained in this study should play an important role in anti-infective macrolide design in the future.

Green and inventive fluorescence approach for levodropropizine determination in human plasma

A green, rapid and sensitive fluorimetric method to quantify levodropropizine (LVP) in human plasma was exploited for the first time. The proposed method adopts LVP's intrinsic fluorescence in distilled water at a detecting emission of 345 nm following excitation at 240 nm. LVP displayed linearity across concentrations ranging from 50 to 1000 ng mL-1, with a detection limit of 0.77 ng mL-1 and a quantification limit of 2.33 ng mL-1. Thorough validation confirmed its reliability, successfully determining LVP in tablets with an average recovery of 98.64 ± 1.07 %. Furthermore, the method's applicability extended to estimate the studied drug in spiked human plasma with excellent obtained percentage recoveries (98.68 ± 1.28-100.14 ± 1.23).

Ratiometric fluorometric assay triggered by alkaline phosphatase: Proof-of-concept toward a split-type biosensing strategy for DNA detection

Herein, a sensitive ratiometric and split-type fluorescent sensing platform has been constructed for DNA detection based on one signal precursor and two fluorescent signal indicators. In this assay, o-phenylenediamine (OPD) was selected as the signal precursor. On one hand, Cu2+ can oxidize OPD to produce 2, 3-diaminophenazine (DAP), which with an emission peak at 555 nm. On the other hand, ascorbic acid (AA) could react with Cu2+ to generate dehydroascorbic acid (DHAA), which could further react with OPD to form 3-(1, 2-dihydroxy ethyl)furo[3, 4-b]quinoxalin-1 (3H)-on (DFQ) with a strong emission peak at 420 nm. As a result, the formation of DAP was inhibited, and leading to the decrease of fluorescence intensity at 555 nm. Alkaline phosphatase (ALP) could catalyze the substrate l-ascorbic acid-2-phosphate (AA2P) to produce AA in situ. Inspired by the successful use of ALP as a biocatalytic marker in bioassay, a split-type ratiometric fluorescent assay has been designed for DNA detection by using H1N1 DNA as the target model. It was realized for ratiometric fluorescent determination of H1N1 in a linear ranging from 50 pM to 1.5 nM with a limit of detection of 10 pM. The novel strategy could reduce the mutual interferences between the biomolecular recognition system and the fluorescence signal conversion system, which improving the accuracy of detection and effectively reducing the background signal. Furthermore, the strategy provided a promising platform for biomarkers detection in the fields of ratiometric fluorescent biosensors and bioanalysis.

Design of a dual Ir-Eu tag for fluorescent visualization and ICP-MS quantification of SIRPα and its host cells

With the expansion of ICP-MS application into the field of bioanalysis, there is an urgent need for novel element tags today. Here, we report the design of a dual-element Ir-Eu tag, opening the door to simultaneous fluorescent imaging and ICP-MS quantification. The ratio of 153Eu/193Ir may serve as a precision control of the labeling process, allowing internal validation of the quantitative results obtained. As for SIRPα and its host cell analysis exemplified here, the Ir-Eu tag demonstrated superior figures of ICP-MS quantification with the LOD (3σ) down to 0.5 (153Eu) and 1.1 (193Ir) pM SIRPα and 220 (153Eu) and 830 (193Ir) RAW264.7 cells more than 130 times more sensitive compared with the LOD (3σ) of 65.2 pM SIRPα at 612 nm using fluorometry. Not limited to these demonstrations, we believe that the design ideas of the dual Ir-Eu tags should be applicable to various cases of bioanalysis when dual optical profiling and ICP-MS quantification are indispensable.

A sensitive fluorometric-colorimetric dual-mode intelligent sensing platform for the detection of formaldehyde

Excess formaldehyde (FA) is a strong carcinogen, so the development of a rapid visualized and portable formaldehyde detection platform is of great research importance. A multi-color fluorescence sensing system constituted of model compound (NAHN) and red-emitting InP/ZnS QDs was constructed herein, which can simultaneously realize fluorometric-colorimetric dual-mode sensing when exposed to FA environment. Its preparation process was simplified, the detection process was green, and the limits of detection (LOD) were 0.623 μM and 0.791 μM, respectively. The high recoveries of FA in actual water samples indicated that the sensor had broad application prospects. The prepared fluorescent film can be utilized for rapid visual simulation analysis of FA on the surface of various fruits and vegetables. In addition, a serial logic gate was designed to quickly semi-quantitatively assess FA concentration, which promoted the realization of on-site intelligent evaluation of FA.

Multicolor emissive carbon dot-based fluorometric analysis platform for rapid quantification and discrimination of nitroimidazole antibiotic residues

The development of efficient, rapid, portable, and accurate analysis of veterinary drug residues in food matrices is in great demand for food safety assessment. Here, we have developed a smartphone-integrated platform for fluorometric quantification of metronidazole (MNZ) residues and constructed a sensor array for discrimination of different nitroimidazole antibiotics (NIIMs). Multicolor CDs (B-CDs, C-CDs, Y-CDs, and R-CD) were prepared and showed different fluorescence response to MNZ. The fluorescence of C-CDs was quenched Because of the inner filter effect (IFE) between the C-CDs and MNZ, while that of R-CDs was enhanced due to the passivation of surface defects by MNZ. Based on the response pattern, the fluorometric quantification of MNZ based on the fluorescence images of C-CD + R-CD system (R/G values) was achieved with a low detection limit of 0.45 μM. By designing a smartphone-integrated platform, the analysis can be completed within 20 min. In addition, a fluorescence sensor array based C-CDs and R-CDs was also developed. The unique fingerprint of each NIIMs was obtained by linear discriminant analysis (LDA) of the response patterns, indicating an effective discrimination of five NIIMs. Moreover, the platform was used for quantification of MNZ in food samples and the recoveries were within 84.0-106.3 % with relative standard deviations 1.2-10.2 %. Therefore, the proposed method shows great potential as a universal platform for rapid detection of veterinary drug residues.

β-Glucuronidase-triggered reaction for fluorometric and colorimetric dual-mode assay based on the in situ formation of silicon nanoparticles

BACKGROUND

β-Glucuronidase (GUS) is considered as a promising biomarker for primary cancer. Thus, the reliable detection of GUS has great practical significance in the discovery and diagnosis of cancer. Compared with traditional organic probes, silicon nanoparticles (Si NPs) have emerged as robust optical nanomaterials due to their facile preparation, superior photobleaching resistance and excellent biocompatibility. However, most nanomaterials-based methods only output a single signal which is easily influenced by external factors in complex systems. Hence, developing nanomaterial-based multi-signal optical assays for highly sensitive GUS determination is still urgently desired.

RESULTS

In this study, we developed a simple and efficient one-step method for the in situ preparation of yellow color and yellow-green fluorescent Si NPs. This was achieved by combining 3-[2-(2-aminoethylamino) ethylamino] propyl-trimethoxysilane with p-aminophenol (AP) in an aqueous solution. The obtained Si NPs showed yellow-green fluorescence at 535 nm when excited at 380 nm, while also exhibiting an absorption peak at a wavelength of 490 nm. Taking inspiration from the easy synthesis step regulated by AP, which is generated through the hydrolysis of 4-aminophenyl β-D-glucuronide catalyzed by GUS, we constructed a direct fluorometric and colorimetric dual-mode method to measure GUS activity. The developed fluorometric and colorimetric sensing platform showed high sensitivity and accuracy with detection limits for GUS determination as low as 0.0093 and 0.081 U/L, respectively.

SIGNIFICANCE

This study provides a facile dual-mode fluorometric and colorimetric approach for determination of GUS activity based on novel Si NPs for the first time. This designed sensing approach was successfully employed for the quantification of GUS in human serum samples and screening of GUS inhibitors, indicating the feasibility and potential applications in clinical cancer diagnosis and anti-cancer drug discovery.

Colorimetric and fluorometric determination of uric acid by a suspension-based assay using enzyme-immobilized micro-sized particles

Daily monitoring of serum uric acid levels is very important to provide appropriate treatment according to the constitution and lifestyle of individual hyperuricemic patients. We have developed a suspension-based assay to measure uric acid by adding a sample solution to the suspension containing micro-sized particles immobilized on uricase and horseradish peroxidase (HRP). In the proposed method, the mediator reaction of uricase, HRP, and uric acid produces resorufin from Amplex red. This resorufin is adsorbed onto enzyme-immobilized micro-sized particles simultaneously with its production, resulting in the red color of the micro-sized particles. The concentration of resorufin on the small surface area of the microscopic particles achieves a colorimetric analysis of uric acid with superior visibility. In addition, ethanol-induced desorption of resorufin allowed quantitative measurement of uric acid using a 96-well fluorescent microplate reader. The limit of detection (3σ) and RSD (n = 3) were estimated to be 2.2 × 10-2 μg/mL and ≤ 12.1%, respectively. This approach could also be applied to a portable fluorometer.

A novel colorimetric and fluorometric dual-signal identification of organics and Baijiu based on nanozymes with peroxidase-like activity

Nanozymes were nanomaterials with enzymatic properties. They had diverse functions, adjustable catalytic activity, high stability, and easy large-scale production, attracting interest in biosensing. However, nanozymes were scarcely applied in Baijiu identification. Herein, a colorimetric and fluorometric dual-signal determination mediated by a nanozyme-H2O2-TMB system was developed for the first time to identify organics and Baijiu. Since the diverse peroxidase-like activity of nanozymes, resulted in different degrees of oxidized TMB. Based on this, 21 organics were identified qualitatively and quantitatively by colorimetric method with a rapid response (<12 min), broad linearity (0.0005-35 mM), and low detection limits (a minimum of 30 nM for glutaric acids). Furthermore, the fluorometric method exhibited excellent potential for accurate determination of organics, with detection ranges of 2-200 µmol/L (LOD: 0.22 µmol/L) for l-ascorbic acid and 2-300 µmol/L (LOD: 0.59 µmol/L) for guaiacol. Finally, the sensor was successfully applied to identify fake Baijiu and Baijiu from 16 different brands.

Highly efficient dual-mode detection of AFB1 based on the inner filter effect: Donor-acceptor selection and application

BACKGROUND

The utilization of inner filter effect (IFE) brings more opportunities for construction of fluorescence immunoassays but remains a great challenge, especially how to select best donor in the face of extensive fluorescent nanomaterials. Aflatoxin B1 possesses high toxicity among mycotoxins and is frequently found in agricultural products that may significantly threaten to human health. Therefore, with the help of signal transduction mechanism of IFE to develop a convenient and sensitive approach for AFB1 detection is of great significance in ensuring food safety.

RESULTS

Herein, the classical alkaline phosphatase (ALP) catalyzes hydrolysis of p-nitrophenylphosphate to produce p-nitrophenol (PNP) was employed as a model reaction, which intends to explore tunable multicolor fluorescence of gold nanoclusters (AuNCs) for matching PNP to maximize IFE efficiency. The luminescent green-emitting AuNCs were selected as an optimal donor in terms of excellent spectral overlap, high photoluminescence, and adequate system adaptability, thus achieving a 22-fold increase in sensitivity improvement compared to colorimetric method for ALP detection. The fluorescence quenching mechanism between PNP and AuNCs was validated as IFE by studying ultraviolet absorption, zeta potentials and fluorescence lifetime. In light of this, we integrated a highly specific antibody-antigen recognition system, efficient enzymatic reaction and excellent optical characteristics of AuNCs to develop dual-mode immunoassay for AFB1 monitoring. The sensitivity of fluorometric immunoassay was lower to 0.06 ng/mL, which obtained a 3.5-fold improvement compared to "gold standard" ELISA. Their practicability and applicability were confirmed in the tap water, corn, wheat and peanuts samples.

SIGNIFICANCE

This work provides an easy-to-understand screening procedure to select optimal donor-acceptor pairs in IFE analysis. Furthermore, we expect that integration of IFE-based signal conversion strategy into mature immunoassay not only extends the signal types, simplifies signal amplification steps, and reduces the false-positive/false-negative rates, but also provides a simple, convenient, and versatile strategy for monitoring of trace other contaminants.

Recent Advances in Gold Nanocluster-Based Biosensing and Therapy: A Review

Gold nanoclusters (Au NCs) with bright emission and unique chemical reactivity characters have been widely applied for optical sensing and imaging. With a combination of surface modifications, effective therapeutic treatments of tumors are realized. In this review, we summarize the recently adopted biosensing and therapy events based on Au NCs. Homogeneous and fluorometric biosensing systems toward various targets, including ions, small molecules, reactive oxygen species, biomacromolecules, cancer cells, and bacteria, in vitro and in vivo, are presented by turn-off, turn-on, and ratiometric tactics. The therapy applications are concluded in three aspects: photodynamic therapy, photothermal therapy, and as a drug carrier. The basic mechanisms and performances of these systems are introduced. Finally, this review highlights the challenges and future trend of Au NC-based biosensing and therapy systems.

Differential scanning fluorimetry to assess PFAS binding to bovine serum albumin protein

The rapid screening of protein binding affinity for poly- and perfluoroalkyl substances (PFAS) benefits risk assessment and fate and transport modelling. PFAS are known to bioaccumulate in livestock through contaminated food and water. One excretion pathway is through milk, which may be facilitated by binding to milk proteins such as bovine serum albumin (BSA). We report a label-free differential scanning fluorimetry approach to determine PFAS-BSA binding over a broad temperature range. This method utilizes the tryptophan residue within the protein binding pocket as an intrinsic fluorophore, eliminating the need for fluorophore labels that may influence binding. BSA association constants were determined by (a) an equilibrium-based model at the melting temperature of BSA and (b) the Hill adsorption model to account for temperature dependent binding and binding cooperativity. Differences in binding between PFAS and fatty acid analogs revealed that a combination of size and hydrophobicity drives PFAS binding.

Combination of gold nanoclusters and silicon quantum dots for ratiometric fluorometry: One system, two mechanisms

A ratiometric fluorometry based on silicon quantum dots (SiQDs) and gold nanoclusters (AuNCs) is constructed for detecting activity of butyrylcholinesterase (BChE) in human serum. By using thiobutyrylcholine iodide (BTCh) as the substrate of BChE-catalyzed hydrolysis reaction, variation of fluorescence emission from AuNCs is employed as an indicator of BChE activity since one of the hydrolysis products, thiocholine (TCh), would influence the aggregation state of AuNCs and consequently led to the change of fluorescence quantum efficiency of AuNCs. It is interesting that there are two mechanisms working for the fluorescence emission of aggregated AuNCs: aggregation-induced emission enhancement (AIEE) and aggregation-caused quenching (ACQ) with the presence of TCh at very low and higher concentration levels, respectively. Although both of these mechanisms can be utilized for sensing BChE, their opposite influence on the fluorescence emission of aggregated AuNCs should be worthy of attention, especially in the process of developing fluorescence methods for detecting trace targets by using AuNCs. In order to eliminate the fluctuation of fluorophotometer, SiQDs is chosen as the fluorophore to develop by ratiometric fluorescence methods in this work. Additionally, obvious aggregation of AuNCs induces significant decrease of inner filter effect (IFE) on the fluorescence emitted from SiQDs, while mild aggregation of AuNCs demonstrates little IFE. The linear ranges for detecting activity of BChE are 0.004 - 0.05 U/L and 0.5 - 20 U/L by ratiometric fluorometry based on the AIEE and ACQ, respectively. The very different responses originated from AIEE and ACQ of AuNCs would respectively make their own contributions to the determination of BChE activities at very low or high levels, which facilitate the developments of enhanced or quenched fluorescence methods. However, the detection of BChE activities at medium levels might suffer from the combination of AIEE and ACQ with ambiguous fractions. Therefore, it must be careful during the processes of developing and applying fluorescence methods based on the AIEE and ACQ of AuNCs, as well as the process of evaluating their analytical performance.

Colorimetric and fluorometric bimodal amine chemosensor based on deprotonation-induced intramolecular charge transfer: Application to food spoilage detection

Amine derivatives are signature organic compounds generated from rotten protein food. Thus, sensitive detection of the presence of amines in protein foods can be a critical technique for monitoring their quality. In this study, we develop an organic chemosensor probe, 4-(2-(3-(dicyanomethylene)- 5,5-dimethylcyclohex-1-en-1-yl)vinyl)-N,N-diethylbenzenaminium chloride (DEAH), to effectively detect amines through discernible bimodal (colorimetric and fluorometric) changes. By exploiting the amine-triggered intramolecular charge transfer behavior, DEAH exhibits rapid color changes (<1 s) with an excellent detection limit (36.9 nM) and also fluorescence turn-on in response to amine gas. Moreover, it possesses detection capabilities in versatile conditions, including solutions, solids, and coated films, suggesting its practical applicability. In particular, DEAH shows dramatic color change from yellow to violet with exceptional color difference (△Eab) over 98, repeatable usability, and excellent selectivity to amines. Based on these compelling advantages, we successfully demonstrate real-time monitoring of amine gas generated from spoiled protein foods using DEAH-coated films.

A near-infrared fluorescent probe for rapid and on-site detection of sulfur dioxide derivative in biological, food and environmental systems

Emission of toxic gaseous sulfur dioxide (SO2) and its derivative bisulfite (HSO3-) from various industrial applications, like food processing, transportation, and the coking process, has raised substantial concerns regarding environmental quality and public health. The probes for specific and sensitive detection of SO2 derivatives plays an essential role in their regulation, and ultimately mitigating their environmental and health implications, but the one that can detect SO2 derivatives onsite by end users remains limited. Herein, we report a new near-infrared fluorescence probe (SL) for rapid and onsite detection of SO2 derivative, HSO3- in industrial wastewater, food samples and for sensing its interaction with biological organisms. The SL is developed through coupling of quinolinium and coumarin moiety through an electron deficit CC bond that can specifically react with HSO3- via a Michael addition. By recording the blue shift of absorption and emission spectra, SL can sensitively detect HSO3- (limit of detection, 38 nM) in aqueous solution within 40 s SL is biocompatible, can be used for evaluating toxicity of SO2 derivatives in living organisms. The preparation of SL-stained test paper allows the colorimetric/fluorometric analysis for quantification of HSO3- onsite in food, river and coking wastewater samples using a smartphone. The successful development of SL not only provides a new tool to investigate HSO3- in biological, food and environmental systems, but also potentially promotes the application of fluorescence technique for rapid and onsite analysis of real-world samples by end users.

Utility of Cilefa Pink B, a foodstuff dye as a fluoro-substrate in the devising of the first facile green Molecular-mass-Related Fluorescence Sensor for quantifying amlodipine in batched material and dosage forms; content uniformity evaluation

This study introduces the first and unique Molecular-mass-Related Fluorescence Sensor as the first fluorimetric strategy for determining amlodipine. An environmentally friendly, single-step, and direct spectrofluorimetric approach was utilized to evaluate the analyte. In an acidic setting, combining the amlodipine medication and the fluorescent dye Cilefa Pink B generated an instantaneous ultra-fluorescent product. An increase in dye response after adding amlodipine was proportional to the molecular weight of the generated complex, as measured at 329 nm. was the idea ofthe applied fluorimetric analysis. The complexing process increased the molecular mass from 879.86 to 1288.739 g mol-1. The medication's range of 0.050-1.00 µg mL-1 is directly correlated with this molecular massenlargement. The ideal settings for the changeable parameters of the system were established through an analysis of the response of the amlodipine-Cilefa Pink B system. Furthermore, the developed sensor complied with ICH (International Council for Harmonization) standards. The sensitivity limits were 0.0139 µg mL-1 (for the detection limit, LOD) and 0.042 µg mL-1 (for the quantification limit, LOQ). Additionally, this method effectively recovered the drug in its original and therapeutic dosage forms. Finally, the proposed process's environmental impact was also assessed through different modern greenness evaluation tools.

PACMan: A software package for automated single-cell chlorophyll fluorometry

Microalgae, small photosynthetic unicells, are of great interest to ecology, ecotoxicology and biotechnology and there is a growing need to investigate the ability of cells to photosynthesize under variable conditions. Current strategies involve hand-operated pulse-amplitude-modulated (PAM) chlorophyll fluorimeters, which can provide detailed insights into the photophysiology of entire populations- or individual cells of microalgae but are typically limited in their throughput. To increase the throughput of a commercially available MICROSCOPY-PAM system, we present the PAM Automation Control Manager ('PACMan'), an open-source Python software package that automates image acquisition, microscopy stage control and the triggering of external hardware components. PACMan comes with a user-friendly graphical user interface and is released together with a stand-alone tool (PAMalysis) for the automated calculation of per-cell maximum quantum efficiencies (= Fv /Fm ). Using these two software packages, we successfully tracked the photophysiology of >1000 individual cells of green algae (Chlamydomonas reinhardtii) and dinoflagellates (genus Symbiodiniaceae) within custom-made microfluidic devices. Compared to the manual operation of MICROSCOPY-PAM systems, this represents a 10-fold increase in throughput. During experiments, PACMan coordinated the movement of the microscope stage and triggered the MICROSCOPY-PAM system to repeatedly capture high-quality image data across multiple positions. Finally, we analyzed single-cell Fv /Fm with the manufacturer-supplied software and PAMalysis, demonstrating a median difference <0.5% between both methods. We foresee that PACMan, and its auxiliary software package will help increase the experimental throughput in a range of microalgae studies currently relying on hand-operated MICROSCOPY-PAM technologies.

Fluorimetric study on a novel FDA-approved combination used for the treatment of overactive bladder syndrome in different matrices

For the first time, two spectrofluorimetric techniques were created for the concurrent determination of mirabegron (MBN) and solifenacin (SOL) in different matrices. This novel combination recently received FDA approval to treat overactive bladder syndrome and was marketed under the brand name MiragoTMS25. SOL has a native fluorescence and can be estimated directly in the presence of MBN without any interference at 290 nm after excitation at 230 nm. In contrast to SOL, MBN is a weak fluorescent substance that requires the use of a fluorogenic reagent (like NBD-Cl) to be measured simultaneously with SOL in their mixtures. So, we reacted MBN with NBD-Cl to yield a yellow-colored fluorophore that could be estimated at 546 nm after excitation at 471 nm without any preliminary separation or interference from SOL. All experimental conditions of the applied methods were tested and enhanced for the best results. The applied fluorimetric methods succeeded in determining both drugs in nanograms, making them applicable in biological fluids like human plasma. The linearity ranges of SOL and MBN were found to be 5-250 ng/mL and 50-600 ng/mL, respectively. The LOD values were 0.96 ng/mL and 5.09 ng/mL for SOL and MBN, in order. Excellent results were attained for both drugs during their analysis in spiked plasma samples employing the applied fluorimetric methods, confirming their suitability for use in real human plasma samples and paving the way for further bioequivalence studies on both drugs.

Fluorometric and colorimetric dual-mode sensing of α-glucosidase based on aggregation-induced emission enhancement of AuNCs

Herein, a fluorometric and colorimetric dual-mode assay platform used for α-glucosidase (α-Glu) activity sensing based on aggregation-induced emission enhancement (AIEE) of AuNCs was developed for the first time. The quantum yield (QY) and fluorescence lifetime of AuNCs were successfully ameliorated by Ce3+-triggered AIEE (Ce@AuNCs). Subsequently, on the basis of the inner filter effect (IFE) and dynamic quenching effect (DQE) between 2,6-dichlorophenolindophenol (DCIP) and Ce@AuNCs as well as the reduction of DCIP by ascorbic acid (AA) generated from α-Glu-catalyzed hydrolysis of L-ascorbic acid-2-O-α-D-glucopyranosyl (AA2G), the marriage of fluorometric and colorimetric modes applied for α-Glu activity monitoring was achieved. Besides, the feasibility of this dual-mode sensing system was confirmed by the assays versus potential interfering substances and in real samples. In particular, this system was further applied to evaluate natural α-Glu inhibitors (AGIs) including luteolin, apigenin, and hesperidin. Overall, the multi-mode optical sensor newly designed here has the potential for the accurate discovery of natural anti-diabetes drugs and the therapy of diabetes.

Dopamine-based selective spectrophotometry p-aminosalicylic acid assay by hydrolyzate-triggered formation of azamonardine-like products

BACKGROUND

The selective recognition of drugs and its metabolism or decomposition products is significant to drug development and drug resistance research. Fluorescence-based techniques provide satisfying sensitivity by target-triggered chemical reaction. However, the interference from the matrix or additives usually restricts the specific detection. It is highly desirable to explore specific chemical reactions for achieving selective perception of these species.

RESULTS

We report a specific m-aminophenol (MAP)-dopamine (DA) reaction, which generates highly fluorescent azamonardine-like products. Based on this reaction, fluorometric and indirect detection of p-aminosalicylic acid (typical antituberculosis drug, PAS) can be realized using the DA-based probe with high sensitivity. The acid induces the decarboxylation of PAS and produces MAP, which reacts with DA and generates fluorescent azamonardine-like products. The practical application of the proposed method is validated by the accurate PAS analysis in urine samples and Pasinazid tablets. Interestingly, none of additives in the Pasinazid tablets contribute comparable fluorescence variation.

SIGNIFICANCE

This work discovers a new MAP-DA reaction for the first time, it not only explores sensitive PAS drug detection probe, but also demonstrates the feasibility of the development of novel drug analysis platform by recognizing decomposition product with specific reaction. Thus, new avenues for the exploration of simple and rapid spectrophotometric probes toward various drug analytes with high specify and sensitivity based on this tactic might be possible in analytical and drug-related fields.

Development of a fluorometric and colorimetric dual-mode sensing platform for acid phosphatase assay based on Fe3+ functionalized CuInS2/ZnS quantum dots

BACKGROUND

The spectral dual-mode response towards analyte has been attracted much attention, benefiting from the higher detection accuracy of such strategy in comparison to single signal readout. However, the currently reported dual-mode sensors for acid phosphatase (ACP) activity are still limited, and most of them more or less exist some deficiencies, such as complicated construction procedure, high-cost, poor biocompatibility, aggregation-caused quenching and limited emission capacity.

RESULTS

Herein, we employed Fe3+ functionalized CuInS2/ZnS quantum dots (CIS/ZnS QDs) as nanosensor to develop a novel fluorometric and colorimetric dual-mode assay for ACP activity, combing with ACP-triggered hydrolysis of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA). The Fe3+ binding to CIS/ZnS QDs can be reduced into Fe2+ during the determination, resulting in the dramatically weakened photoinduced electron transfer (PET) effect and the disappearance of competition absorption. Thus, a highly sensitive ACP assay in the range of 0.22-12.5 U L-1 through fluorescence "turn-on" mode has been achieved with a detection of limit (LOD) of 0.064 U L-1. Meanwhile, the ACP activity can also be quantified by spectrophotometry based on the chromogenic reaction of the formed Fe2+ with 1,10-phenanthroline (Phen). Moreover, the designed nanosensor with good biocompatibility was successfully applied to image and monitor the ACP levels in living cells.

SIGNIFICANCE

We believe that the proposed method has remarkable advantages and potential application for ACP assay in terms of the high accuracy, simplicity, low cost, as well as its adequate sensitivity.

Analysis of platinum-based anticancer injections cisplatin and carboplatin in blood serum and urine of cancer patients by photometry, fluorometry, liquid chromatography using a Schiff-base as derivatizing reagent

Photometric, fluorometric and liquid chromatographic methods were proposed to analyze Pt(II) from cis-platin and carbo-platin injections after derivatization with reagent 2-oxo-propanoic acid N-phenylhydrazonecarbothioamide. The reagent reacted with metals Au(III), Ag(I), Mn(II), Pt(II), Mo(VI), V(V/IV) to develop their characteristic colors in the pH range 3-12 and were extracted in organic solvent trichloromethane. The photoluminescent behavior of ligand and its metal complexes was investigated to correlate the emission pattern. Liquid chromatographic method was also proposed to analyze cis-platin and carbo-platin anti-cancer drugs based on the pre-column derivatizing platinum(II) with ligand. The complex of platinum was separated and eluted from HPLC column Microsorb C-18, (150 cm x 4.6 mm i.d, 5 µm) comprising eluents - tetrabutyl ammonium bromide (1 mM)-sodium acetate (1 mM)-acetonitrile-water-methanol (02:02:06:22:68 v/v/v/v/v). Metals Au(III), Ag(I), Mn(II), V(IV/V), Mo(VI) were also separated completely. The linear calibration range 0.5-2.5 µg/mL was observed following Beer's law with detection limit of 150.00 ng/mL Pt(II). The determination of cis-platin and carbo-platin injections by photometric, fluorometric and chromatographic methods showed RSD (n = 3) 1.14-3.12, 0.98-2.84, 0.92-2.72% respectively. The developed methods were employed to analyze cis-platin in samples of serum and urine of cancer patients undergoing chemotherapy and platinum amounts were observed within 45.0-86.0, 49.0-91.0, 42.0-84.0 ng/mL and 82.0-398, 81.0-389, 74.0-391 ng/mL with relative standard deviation (RSD) (n = 4) of 2.28-3.88, 2.40-3.82, 2.52-3.82% and 2.52-3.91, 2.44-3.94, 1.98-3.24% by liquid chromatographic, fluorometric and photometric techniques respectively.

Fluorimetric Cell Analysis with 9-Aryl-Substituted Berberine Derivatives as DNA-Targeting Fluorescent Probes

DNA-sensitive fluorescent light-up probes based on berberine are presented. This biogenic fluorophore was chosen as central unit to use its potential biocompatibility and its DNA-binding properties. To provide predictable fluorescence quenching in aqueous solution and a fluorescence light-up effect upon DNA binding, aryl substituents were attached at the 9-position by Suzuki-Miyaura coupling reactions. The 9-arylberberine derivatives have a very low fluorescence quantum yield (Φfl =<0.02), which is caused by the radiationless deactivation of the excited state by torsional relaxation about the biaryl axis. In addition, these berberine derivatives intercalate into DNA with high affinity (Kb =2.0-22×104  M-1 ). Except for the nitrophenyl- and hydroxyphenyl-substituted derivatives, all tested compounds exhibited a pronounced fluorescence light-up effect upon association with DNA, because the deactivation of the excited-state by torsional relaxation is suppressed in the DNA binding site. Most notably, it was shown exemplarily with the 9-(4-methoxyphenyl)- and the 9-(6-methoxynaphthyl)-substituted derivatives that these properties are suited for fluorimetric cell analysis. In particular, these probes generated distinct staining patterns in eukaryotic cells (NIH 3T3 mouse fibroblasts), which enabled the identification of nuclear substructures, most likely heterochromatin or nucleoli, respectively.

Dual-mode colorimetric and fluorescence biosensors for the detection of foodborne bacteria

Due to the growing demand for detection technologies, there has been significant interest in the development of integrated dual-modal sensing technologies, which involve combining two signal transduction channels into a single technique, particularly in the context of food safety. The integration of two detection signals not only improves diagnostic performance by reducing assumptions, but also enhances diagnostic functions with increased application flexibility, improved accuracy, and a wider detection linear range. The top two output signals for emerging dual-modal probes are fluorescent and colorimetric, due to their exceptional advantages for real-time sensitive sensing and point-of-care applications. With the rapid progress of nanotechnology and material chemistry, the integrated colorimetric/fluorimetric dual-mode systems show immense potential in sensing foodborne pathogenic bacteria. In this comprehensive review, we present a detailed summary of various colorimetric and fluorimetric dual-modal sensing methods, with a focus on their application in detecting foodborne bacteria. We thoroughly examine the sensing methodologies and the underlying principles of the signal transduction systems, and also discuss the challenges and future prospects for advancing research in this field.

Fenton-like reaction triggered chemical redox-cycling signal amplification for ultrasensitive fluorometric detection of H2O2 and glucose

An ultrasensitive fluorescent biosensor is reported for glucose detection based on a Fenton-like reaction triggered chemical redox-cycling signal amplification strategy. In this amplified strategy, Cu2+ oxidizes chemically o-phenylenediamine (OPD) to generate photosensitive 2,3-diaminophenazine (DAP) and Cu+/Cu0. On the one hand, the generated Cu0 catalyzes the oxidation of OPD. On the other hand, H2O2 reacts with Cu+ to produce hydroxyl radicals (˙OH) and Cu2+ through a Cu+-mediated Fenton-like reaction. The generated ˙OH and recycled Cu2+ ions take turns oxidizing OPD to produce more photoactive DAP, triggering a self-sustaining chemical redox-cycling reaction and a remarkable fluorescent enhancement. It is worth mentioning that the cascade reaction did not stop until OPD molecules were completely consumed. Benefiting from H2O2-triggered chemical redox-cycling signal amplification, the strategy was exploited for the development of an ultrasensitive fluorescent biosensor for glucose determination. Glucose content monitoring was realized with a linear range from 1 nM to 1 μM and a limit of detection of 0.3 nM. This study validates the practicability of the chemical redox-cycling signal amplification on the fluorescent bioanalysis of glucose in human serum samples. It is expected that the method offers new opportunities to develop ultrasensitive fluorescent analysis strategy.

Dark nanodiscs for evaluating membrane protein thermostability by differential scanning fluorimetry

Measuring protein thermostability provides valuable information on the biophysical rules that govern the structure-energy relationships of proteins. However, such measurements remain a challenge for membrane proteins. Here, we introduce a new experimental system to evaluate membrane protein thermostability. This system leverages a recently developed nonfluorescent membrane scaffold protein to reconstitute proteins into nanodiscs and is coupled with a nano-format of differential scanning fluorimetry (nanoDSF). This approach offers a label-free and direct measurement of the intrinsic tryptophan fluorescence of the membrane protein as it unfolds in solution without signal interference from the "dark" nanodisc. In this work, we demonstrate the application of this method using the disulfide bond formation protein B (DsbB) as a test membrane protein. NanoDSF measurements of DsbB reconstituted in dark nanodiscs loaded with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dimyristoyl-sn-glycero-3-phosphorylglycerol (DMPG) lipids show a complex biphasic thermal unfolding pattern with a minor unfolding transition followed by a major transition. The inflection points of the thermal denaturation curve reveal two distinct unfolding midpoint melting temperatures (Tm) of 70.5°C and 77.5°C, consistent with a three-state unfolding model. Further, we show that the catalytically conserved disulfide bond between residues C41 and C130 drives the intermediate state of the unfolding pathway for DsbB in a DMPC and DMPG nanodisc. To extend the utility of this method, we evaluate and compare the thermostability of DsbB in different lipid environments. We introduce this method as a new tool that can be used to understand how compositionally and biophysically complex lipid environments drive membrane protein stability.

A SYBR Green I-based aptasensor for the label-free, fluorometric, and anti-interference detection of MeHg. Anal Bioanal Chem 2024;416:299-311. [PMID: 37932512 DOI: 10.1007/s00216-023-05018-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Methylmercury (MeHg+) is a common form of organic mercury that is substantially more toxic than inorganic mercury and is more likely to accumulate in organisms through biological enrichment. Therefore, developing a method to enable the specific and rapid detection of MeHg+ in seafood is important and remains challenging to accomplish. Herein, a rapid, label-free fluorescence detection method for MeHg+ determination was developed based on SYBR Green I. The detection system implemented "add and measure" detection mode can be completed in 10 min. Under optimal assay conditions, the detection platform showed a linear relationship with the concentration of MeHg+ within 1-50 nM (Y = 8.573x + 42.89, R2 = 0.9928), with a detection limit of 0.3218 nM. The results obtained for competitive substances, such as inorganic mercury ions and anions, show a high specificity of the method. In addition, this method successfully detected MeHg+ in seawater and marine products, with an accompanying spike recovery rate of 96.45-105.1%.

Towards new fluorometric methodologies based on the in-situ generation of gold nanoclusters

In this manuscript a method for the fluorometric determination of tyramine is described. It is based on the direct reaction between Au(III) and tyramine in a phosphate buffer which produces fluorescent gold nanoclusters (AuNC) (λexc = 320 nm, λem = 410 nm) with a diameter of 1.50 ± 0.06 nm. The Au(III) and buffer solutions are mixed and after 140 s, tyramine solution is added; which produces a fast and stable fluorescence signal. The formation of AuNC is demonstrated by STEM and, more importantly, this reaction could be followed by Atomic Fluorescence Microscopy (AFM). The method allows the determination of tyramine in the range from 6.0x10-7 M (limit of quantification) up to 1.2x10-4 M; with a relative standard deviation (RSD) ranges from 1.8% to 4.4% depending on the tyramine concentration. The mechanism of AuNC formation involves the Au(III) reduction via the phenol group and the complexation with the amine group. Putrescine and cadaverine do not produce interference, meanwhile histamine causes a proportional decrease in the signal which can be overcome by the standard addition method. The method was applied to the determination of tyramine in a tuna and cheese samples and the results obtained are in statistical agreement with these obtained using a validated or standard method.

A Study of Small Molecule-Based Rhodamine-Derived Chemosensors and their Implications in Environmental and Biological Systems from 2012 to 2021: Latest Advancement and Future Prospects

Rhodamine-based chemosensors have sparked considerable interest in recent years due to their remarkable photophysical properties, which include high absorption coefficients, exceptional quantum yields, improved photostability, and significant red shifts. This article presents an overview of the diverse fluorometric, and colorimetric sensors produced from rhodamine, as well as their applications in a wide range of fields. The ability of rhodamine-based chemosensors to detect a wide range of metal ions, including Hg+2, Al3+, Cr3+, Cu2+, Fe3+, Fe2+, Cd2+, Sn4+, Zn2+, and Pb2+, is one of their major advantages. Other applications of these sensors include dual analytes, multianalytes, and relay recognition of dual analytes. Rhodamine-based probes can also detect noble metal ions such as Au3+, Ag+, and Pt2+. They have been used to detect pH, biological species, reactive oxygen and nitrogen species, anions, and nerve agents in addition to metal ions. The probes have been engineered to undergo colorimetric or fluorometric changes upon binding to specific analytes, rendering them highly selective and sensitive by ring-opening via different mechanisms such as Photoinduced Electron Transfer (PET), Chelation Enhanced Fluorescence (CHEF), Intramolecular Charge Transfer (ICT), and Fluorescence Resonance Energy Transfer (FRET). For improved sensing performance, light-harvesting dendritic systems based on rhodamine conjugates has also been explored for enhanced sensing performance. These dendritic arrangements permit the incorporation of numerous rhodamine units, resulting in an improvement in signal amplification and sensitivity. The probes have been utilised extensively for imaging biological samples, including imaging of living cells, and for environmental research. Moreover, they have been combined into logic gates for the construction of molecular computing systems. The usage of rhodamine-based chemosensors has created significant potential in a range of disciplines, including biological and environmental sensing as well as logic gate applications. This study focuses on the work published between 2012 and 2021 and emphasises the enormous research and development potential of these probes.

Quantitative Biochemical Analysis of Deadenylase Enzymes Using Fluorescence and Chemiluminescence-Based Assays

Deadenylase enzymes play a key role in mRNA degradation and RNA processing. In this chapter, we describe two activity assays for the quantitative biochemical analysis of deadenylase enzymes, which can easily be adapted for other nuclease enzymes. The assays use distinct principles of detection, which are based on differential annealing of a probe complementary to the substrate RNA or detection of adenosine monophosphate (AMP). The assays are sensitive, flexible, and can be used in low-throughput tube-based formats and 96-well or 384-well plate formats. The assays rely on plate reader detection and can be carried out using manual pipetting or robotic liquid handling equipment. In addition to two activity assays, we describe differential scanning fluorimetry (thermal shift assay) as a complementary assay that allows the direct characterization of ligand binding to deadenylase enzymes. The assays can be useful for the characterization of deadenylase variants and are particularly suitable for the discovery and development of small-molecule inhibitors of deadenylase enzymes.

Fe-Ni dual-single atoms nanozyme with high peroxidase-like activity for sensitive colorimetric and fluorometric dual-mode detection of cholesterol

Cholesterol is widely existed in nerve myelin sheath and various membrane structures, whose abnormal level would deteriorate human cells or even cause diseases. Herein, Fe-Ni dual-single-atom nanozyme was efficiently incorporated into N-doped carbon nanosheets (FeNi DSAs/N-CSs) by a simple calcination method. Its nanozyme activity and catalytic mechanism were investigated in details. The FeNi DSAs/N-CSs nanozyme showed superior peroxidase-like property, which was applied for the dual-mode determination of hydrogen peroxide (H2O2) and cholesterol. The colorimetric/fluorometric assays of H2O2 displayed the linear ranges of 1-50 mM and 5-40 mM with low limits of detection of 0.45 mM and 3.33 mM, respectively. In parallel, there exhibited the linear ranges of 0.5-5.0 mM and 0.25-5.0 mM for the colorimetric/fluorometric analysis of cholesterol, coupled with the limits of detection down to 0.19 mM and 0.044 mM, respectively. This work provided a rapid, cost-effectiveness and simple colorimetric/fluorometric method for sensitive dual-mode detection of cholesterol in human serum samples.

Protein arginine N-methyltransferase 2 plays a noncatalytic role in the histone methylation activity of PRMT1

Protein arginine N-methyltransferases are a family of epigenetic enzymes responsible for monomethylation or dimethylation of arginine residues on histones. Dysregulation of protein arginine N-methyltransferase activity can lead to aberrant gene expression and cancer. Recent studies have shown that PRMT2 expression and histone H3 methylation at arginine 8 are correlated with disease severity in glioblastoma multiforme, hepatocellular carcinoma, and renal cell carcinoma. In this study, we explore a noncatalytic mechanistic role for PRMT2 in histone methylation by investigating interactions between PRMT2, histone peptides and proteins, and other PRMTs using analytical and enzymatic approaches. We quantify interactions between PRMT2, peptide ligands, and PRMT1 in a cofactor- and domain-dependent manner using differential scanning fluorimetry. We found that PRMT2 modulates the substrate specificity of PRMT1. Using calf thymus histones as substrates, we saw that a 10-fold excess of PRMT2 promotes PRMT1 methylation of both histone H4 and histone H2A. We found equimolar or a 10-fold excess of PRMT2 to PRMT1 can improve the catalytic efficiency of PRMT1 towards individual histone substrates H2A, H3, and H4. We further evaluated the effects of PRMT2 towards PRMT1 on unmodified histone octamers and mononucleosomes and found marginal PRMT1 activity improvements in histone octamers but significantly greater methylation of mononucleosomes in the presence of 10-fold excess of PRMT2. This work reveals the ability of PRMT2 to serve a noncatalytic role through its SH3 domain in driving site-specific histone methylation marks.

Two fluorimetric determinations of acid α-glucosidase activity in dried blood spot: Pompe disease in Iranian population

INTRODUCTION

Pompe disease is a lysosomal storage disorder. This study aimed to validate and compare 2 fluorimetric methods for measuring α-glucosidase acid activity in dried blood spot sample (DBS), with potential applications in neonatal screening, and disease follow-up of Pompe patients among the Iranian population for the first time.

MATERIALS AND METHODS

The evaluation involved 3 enzyme levels and 7 parameters. The analysis included 141 Healthy individuals, 8 Pompe patients, and 10 obligate heterozygotes using reference and modified methods.

RESULTS

Both methods exhibited highly linear calibration curves. The limit of detection (LOD) and limit of quantification (LOQ) were obtained in the micromolar concentration range in 2 methods. Inter-day and intra-day precision, expressed as relative standard deviations (RSD%) were calculated. The normal ranges were determined in healthy individuals. Receiver operating characteristic (ROC) curves were analyzed, and 2 parameters, total neutral α-glucosidase (NAG)/acid α-glucosidase (GAA) and pH ratio, were identified as cut-off values with excellent accuracy, sensitivity, and specificity for evaluating Pompe disease in both methods.

CONCLUSIONS

Establishing and implementing these 2 methods for the Iranian population effectively differentiated between healthy and patient individuals. Method II, with its shorter incubation time, demonstrated practicality in the clinical setting.

Direct fluorescence labelling of NO inside plant cells

Nitric oxide (NO) plays a key role in regulating plant growth, enhances nutrient uptake, and activates disease and stress tolerance mechanisms in most plants. NO is marked as a potential tool for improving the yield and quality of horticultural crop species. Research on NO in plant species can provide an abundance of valuable information regarding this. Hence, we have prepared a simple chemosensor (NPO) for the detection of endogenous NO in chickpea saplings. NPO selectively interacts with NO as determined through a chemodosimetric method to clearly show both the colorimetric and fluorometric changes. After the interaction with NO, the colorless NPO turns yellow as observed by the naked eye and shows bright cyan-blue fluorescence under a UV lamp. The 1 : 1 stoichiometric ratio between NPO and NO is determined from Job's plot resulting in a stable diazeniumdiolate product. The interaction mechanism is well established by absorption, fluorescence titration, NMR titration, HRMS, and DFT calculations. This method has successfully been employed in the plant's root and stem systems to label NO. Confocal microscopy images might help us to understand the endogenous NO generation and the mechanism that happens inside plant tissues.

Galvanic Bipolar Electrode Arrays with Self-Driven Optical Readouts

In this work, we report a bipolar electrode (BPE) array system with self-driven optical readouts of the faradic current flowing through the BPEs. The BPE array system is based on the spontaneous redox reactions that are respectively occurring at opposite poles of the BPEs with appropriate electrocatalysts on the poles; this system is analogous to one consisting of galvanic electrochemical cells. The galvanic BPE array system operates in a self-powered mode that requires there to be neither a direct electrical connection nor external electrical polarization to each BPE. Importantly, the appropriate electrocatalysts on the poles play a critical role in the galvanic BPE array system to induce the spontaneous redox reactions occurring at the poles of BPEs. Moreover, the galvanic BPE array system provides self-driven optical readouts, including fluorometric and colorimetric ones, to report the faradaic current resulting from the spontaneous redox reactions on the BPE poles. Based on the unique benefits that the galvanic BPE array system has over conventional BPEs, we demonstrated the promising potential of galvanic BPE arrays for the simple yet rapid and quantitative screening of electrocatalysts for the oxygen reduction reaction as well as sensitive sensing of H2O2 in parallel.

Isothermal chemical denaturation assay for monitoring protein stability and inhibitor interactions

Thermal shift assay (TSA) with altered temperature has been the most widely used method for monitoring protein stability for drug research. However, there is a pressing need for isothermal techniques as alternatives. This urgent demand arises from the limitations of TSA, which can sometimes provide misleading ranking of protein stability and fail to accurately reflect protein stability under physiological conditions. Although differential scanning fluorimetry has significantly improved throughput in comparison to differential scanning calorimetry and differential static light scattering throughput, all these methods exhibit moderate sensitivity. In contrast, current isothermal chemical denaturation (ICD) techniques may not offer the same throughput capabilities as TSA, but it provides more precise information about protein stability and interactions. Unfortunately, ICD also suffers from limited sensitivity, typically in micromolar range. We have developed a novel method to overcome these challenges, namely throughput and sensitivity. The novel Förster Resonance Energy Transfer (FRET)-Probe as an external probe is highly applicable to isothermal protein stability monitoring but also to conventional TSA. We have investigated ICD for multiple proteins with focus on KRASG12C with covalent inhibitors and three chemical denaturants performed at nanomolar protein concentration. Data showed corresponding inhibitor-induced stabilization of KRASG12C to those reported by nucleotide exchange assay.

Determination of Selenium in Selenium-Enriched Products by Specific Ratiometric Fluorescence

Selenium (Se), as one of the essential and nutrient components of living organisms and plants, plays an important role in life activities, while excessive selenium is hazardous to human health. So, the establishment of an effective method for simple, rapid, and highly sensitive determination of selenium content is crucial in the field of food composition analysis and other areas. In this paper, a novel and simple ratiometric fluorescence method for the determination of Se has been developed using 9-anthracenemethanol (AM) as the ratiometric fluorescence reagent on the basis of the conventional fluorometric assay which utilized 2,3-diaminonapthalene (DAN) as fluorescent ligand. The ratiometric method was compared with the conventional method with respect to precision and accuracy. The inter-day and intra-day precisions (RSDs) of the ratiometric fluorescence method ranged from 2.08 to 2.78% and 1.28 to 1.84%, with mean recoveries of 93.2~98.0% and limit of detection (LOD) and limit of quantification (LOQ) of 0.0016 and 0.0049 μg/mL, respectively. This method was successfully applied to the determination of total selenium in selenium-enriched milk and selenium-supplemented shampoo, with the results in agreement with those obtained by inductively coupled plasma mass spectrometer (ICP-MS). The results demonstrated that the precision and accuracy of the ratiometric fluorescence method were superior to those of the conventional fluorescence method, and the interferences of various environmental factors were effectively eliminated. The precision and accuracy of the conventional method can be significantly improved by simply adding an elaborately selected ratiometric fluorescence reagent, and the new method will have broader practical applications.

Sonochemical Synthesized Manganese Oxide Nanoparticles as Fluorescent Sensor for Selenium (IV) Quantification. Application to Food and Drink Samples

Manganese oxide nanoparticles (MnO Nps), sonochemical synthesized and characterized in our laboratory, are proposed as fluorescent sensor for selenium (Se) determination. The new methodology has been developed based on the enhancing effect of the Se(IV) on fluorescent emission of MnO Nps. Experimental variables that influence on fluorimetric sensitivity were optimized. The calibration graph using zeroth order regression was linear from 0.189 ng L-1 to 8.00 × 103 µg L-1, with correlation coefficient better than 0.99. Under the optimal conditions, the limits of detection and quantification were of 0.062 ng L-1 and 0.189 ng L-1, respectively. The trueness of the methodology was assessed through standard addition method obtaining recovery near to 100%. This method showed good tolerance to foreign ions, particularly to Se(VI), and was applied to determination of Se(IV) trace in food and drink samples with satisfactory results. With the intention of preserving the environment from harmful effects, a degradation study of the used nanomaterials has been included for their subsequent disposal.

Quantitation of autoinhibitory defects in pathogenic SHP2 mutants by differential scanning fluorimetry

Src-homology-2-domain-containing protein tyrosine phosphatase-2 (SHP2) is a signaling enzyme whose activity is governed by an equilibrium between autoinhibited and activated states. Regulation of SHP2 activity is critical for cellular homeostasis, and mutations that alter its autoregulatory equilibrium cause cancers and developmental disorders. Several methods for assessing the strength of autoinhibitory interactions in SHP2 mutants have been previously reported, but each has limitations. We show that differential scanning fluorimetry provides a rapid, quantitative measure of SHP2 autoinhibition that is independent of the intrinsic activity of the SHP2 mutant being analyzed, does not involve protein labeling, and does not require specialized instrumentation.

Fluorometric detection of alpha-fetoprotein based on the use of a novel organic compound with AIE activity and aptamer-modified magnetic microparticles

BACKGROUND

Liver cancer is one of the most common cancers in the world, and it seriously threatens human life and health. Alpha-fetoprotein (AFP), as a carcinogenic glycoprotein, is an important serum marker for detecting liver cancer. Therefore, the accurate and sensitive determination of AFP is crucial for the early diagnosis and treatment of liver cancer. To this end, a label-free fluorescence aptasensor for detecting AFP based on the use of a novel organic Compound D with an aggregation-induced emission activity and aptamer-modified magnetic microparticles was constructed.

RESULTS

Compound D could combine with the complementary short chain of the aptamer (CSC-Apt) of AFP to form the D/CSC-Apt complex and realize the fluorescence enhancement of Compound D. Then, magnetic particles modified by the Apt of AFP (Apt-Fe3O4) were prepared. When AFP (or nontarget substance) and D/CSC-Apt were successively added to the Apt-Fe3O4 solution, Apt-Fe3O4 selectively bound to AFP or the D/CSC-Apt complex. Magnetic separation technology showed the changes in the fluorescence intensity of the supernatant. The research results revealed a good linear relationship between the changes in the fluorescence intensity of the supernatant and concentration of AFP within the concentration range of 10-10000 pg mL-1. The proposed aptasensor could achieve high-sensitivity and high-specificity detection of AFP, and its limit of detection was 3 pg mL-1 (S/N = 3).

SIGNIFICANCE AND NOVELTY

The sensor combines the advantages of high selectivity of Apt, high sensitivity of fluorescence analysis, AIE effect and good water solubility of Compound D, and rapid separation using magnetic separation technology. And it can be directly used for the detection of AFP in actual serum samples with high accuracy, whereas most of the methods reported in the literature can only detect AFP in spiked serum samples.

An eco-friendly fluorometric assay for high-sensitive meloxicam quantitation in biological matrices

Meloxicam (Mel), as a powerful and effective anti-inflammatory drug, is commonly employed for the treatment of various inflammatory diseases; however, the use of Mel at high doses or for extended periods could cause severe side effects in human visceral organs. Therefore, a simple, rapid, and reliable method is urgently needed to monitor Mel in biological samples. Herein, novel water-soluble luminescent nano-carbon dots (nano-Cdots) with outstanding physicochemical properties were prepared by a one-pot high-temperature hydrothermal process of ellagic acid and guanidine. The nano-Cdots were further used as an optical probe for the sensitive detection of Mel in serum samples through the cooperative mechanisms of the inner filter effect and photoelectron transfer. By employing this sensor, an excellent linear correlation was achieved between the relative luminescent intensity [(PL0 - PL)/PL0] and the concentration of Mel in the range of 0.1 to 200 μM, with a limit of detection of 34.68 nM (3σ/k). This sensor was effectively employed for the analysis of Mel in real serum samples, implying its potential development prospects for the advancement of drug analysis with carbon-based probes.

Next Generation of Fluorometric Protease Assays: 7-Nitrobenz-2-oxa-1,3-diazol-4-yl-amides (NBD-Amides) as Class-Spanning Protease Substrates

Fluorometric assays are one of the most frequently used methods in medicinal chemistry. Over the last 50 years, the reporter molecules for the detection of protease activity have evolved from first-generation colorimetric p-nitroanilides, through FRET substrates, and 7-amino-4-methyl coumarin (AMC)-based substrates. The aim of further substrate development is to increase sensitivity and reduce vulnerability to assay interferences. Herein, we describe a new generation of substrates for protease assays based on 7-nitrobenz-2-oxa-1,3-diazol-4-yl-amides (NBD-amides). In this study, we synthesized and tested substrates for 10 different proteases from the serine-, cysteine-, and metalloprotease classes. Enzyme- and substrate-specific parameters as well as the inhibitory activity of literature-known inhibitors confirmed their suitability for application in fluorometric assays. Hence, we were able to present NBD-based alternatives for common protease substrates. In conclusion, these NBD substrates are not only less susceptible to common assay interference, but they are also able to replace FRET-based substrates with the requirement of a prime site amino acid residue.

A facile and eco-friendly fluorometric method for the determination of methotrexate and folic acid in biological samples based on hollow luminescent carbon dots and chemometrics method

A rapid, simple, and inexpensive spectrofluorimetric sensor has been developed for the simultaneous determination of methotrexate (MTX) and folic acid (FA) based on their interactions with hollow carbon dots (HCDs). Since the use of folic acid to cope with the toxic side effects of MTX in patients is essential, the simultaneous determination of these two compounds has been interesting. The results showed that  MTX could quench the fluorescence of HCDs with a dynamic quenching mechanism. The sensor exhibited a linear concentration range of 1.0 × 10-6-1.9 × 10-4 mol L-1 for MTX and 1.5 × 10-5-9.4 × 10-4 mol L-1 for FA and the obtained detection limits for MTX and FA were 1.6 × 10-7 and 5.0 × 10-7 mol L-1, respectively. The applicability of the method was investigated in the analysis of the urine samples and the partial least squares (PLS) method was used for the simultaneous determination of MTX and FA.

A Novel Design Eco-friendly Microwave-assisted Cu-N@CQDs Sensor for the Quantification of Eravacycline via Spectrofluorimetric Method; Application to Greenness Assessments, Dosage Form and Biological Samples

Community-acquired pneumonia is one of the most common infectious diseases and a substantial cause of mortality and morbidity worldwide. Therefore eravacycline (ERV) was approved by the FDA in 2018 for the treatment of acute bacterial skin infections, GIT infections, and community-acquired bacterial pneumonia caused by susceptible bacteria. Hence, a green highly sensitive, cost-effective, fast, and selective fluorimetric approach was developed for the estimation of ERV in milk, dosage form, content uniformity, and human plasma. The selective method is based on the utilization of plum juice and copper sulphate for the synthesis of green copper and nitrogen carbon dots (Cu-N@CDs) with high quantum yield. The quantum dots' fluorescence was enhanced after the addition of ERV. The calibration range was found to be in the range 1.0 - 80.0 ng mL-1 with LOQ equal to 0.14 ng mL-1 and LOD was found to be 0.05 ng mL-1. The creative method is simple to deploy in clinical labs and therapeutic drug health monitoring system. The current approach has been bioanalytically validated using US-FDA and validated ICH criteria. High-resolution transmission electron microscopy (HR-TEM), X-ray photon spectroscopy (XPS), Zeta potential measurements, fluorescence, UV-VIS, and FTIR spectroscopy have all been used to fully characterize the Cu-N@CQDs. The Cu-N@CQDs were effectively applied in human plasma and milk samples with a high percentage of recovery ranging from 97.00 to 98.80%.

Force-induced motions of the PIEZO1 blade probed with fluorimetry

Mechanical forces are thought to activate mechanosensitive PIEZO channels by changing the conformation of a large transmembrane blade domain. Yet, whether different stimuli induce identical conformational changes in this domain remains unclear. Here, we repurpose a cyclic permuted green fluorescent protein as a conformation-sensitive probe to track local rearrangements along the PIEZO1 blade. Two independent probes, one inserted in an extracellular site distal to the pore and the other in a distant intracellular proximal position, elicit sizable fluorescence signals when the tagged channels activate in response to fluid shear stress of low intensity. Neither cellular indentations nor osmotic swelling of the cell elicit detectable fluorescence signals from either probe, despite the ability of these stimuli to activate the tagged channels. High-intensity flow stimuli are ineffective at eliciting fluorescence signals from either probe. Together, these findings suggest that low-intensity fluid shear stress causes a distinct form of mechanical stress to the cell.

A dual-targeting nanobiosensor for Gender Determination applying Signal Amplification Methods and integrating Fluorometric Gold and Silver Nanoclusters

A dual-targeting nanobiosensor has been developed for the simultaneous detection of AMELX and AMELY genes based on the different fluorescence signals emitted from gold and silver nanoclusters, AuNCs and AgNCs respectively. In our design, both catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) have been used as isothermal, enzyme-free and simple methods for signal's amplification. The working principle is based on the initiation of a cascade of CHA-HCR reactions when AMELX is present, in which AuNCs, synthesized on the third hairpin, are aggregated on the surface of the dsDNA product, performing the phenomenon of aggregation induced emission (AIE) and enhancing their fluorescence signal. On the other hand, the presence of the second target, AMELY, is responsible for the enhancement of the fluorescence signal corresponding to AgNCs by the same phenomenon, via hybridizing to the free end of the dsDNA formed and at the same time to the probe of silver nanoclusters fixing it closer to the surface of the dsDNA product. Such a unique design has the merits of being simple, inexpensive, specific and stable and presents rapid results. The detection limits of this assay for AMELX and AMELY are as low as 3.16 fM and 23.6 fM respectively. Moreover, this platform showed great performance in real samples. The design has great promise for the application of dual-targeting nanobiosensors to other biomarkers.

Spectrophotometric and Fluorimetric High-Throughput Assays for Phenolic Acid Decarboxylase

Biocatalytic decarboxylation of hydroxycinnamic acids yields phenolic styrenes, which are important precursors for antioxidants, epoxy coatings, adhesives and other polymeric materials. Bacillus subtilis decarboxylase (BsPAD) is a cofactor-independent enzyme that catalyzes the cleavage of carbon dioxide from p-coumaric-, caffeic-, and ferulic acid with high catalytic efficiency. Real-time spectroscopic assays for decarboxylase reactions remove the necessity of extensive sample workup, which is required for HPLC, mass spectrometry, gas chromatography, or NMR methods. This work presents two robust and sensitive assays based on photometry and fluorimetry that allow decarboxylation reactions to be followed with high sensitivity while avoiding product extraction and long analysis times. Optimized assay procedures were used to measure BsPAD activity in cell lysates and to determine the kinetic constants (KM and Vmax ) of the purified enzyme for p-coumaric-, caffeic- and ferulic acid. Substrate inhibition was shown for caffeic acid.

A fluorometric assay to determine labile copper(II) ions in serum

Labile copper(II) ions (Cu2+) in serum are considered to be readily available for cellular uptake and to constitute the biologically active Cu2+ species in the blood. It might also be suitable to reflect copper dyshomeostasis during diseases such as Wilson's disease (WD) or neurological disorders. So far, no direct quantification method has been described to determine this small Cu2+ subset. This study introduces a fluorometric high throughput assay using the novel Cu2+ binding fluoresceine-peptide sensor FP4 (Kd of the Cu2+-FP4-complex 0.38 pM) to determine labile Cu2+ in human and rat serum. Using 96 human serum samples, labile Cu2+was measured to be 0.14 ± 0.05 pM, showing no correlation with age or other serum trace elements. No sex-specific differences in labile Cu2+ concentrations were noted, in contrast to the total copper levels in serum. Analysis of the effect of drug therapy on labile Cu2+ in the sera of 19 patients with WD showed a significant decrease in labile Cu2+ following copper chelation therapy, suggesting that labile Cu2+ may be a specific marker of disease status and that the assay could be suitable for monitoring treatment progress.

Eco-friendly-assessed micellar-fluorimetric platform for concurrent analysis of empagliflozin and prucalopride succinate in biological fluids: Docking simulation

Fluorescence spectroscopy has an important role in the determination of very small quantities of substances, especially in biological fluids. For this reason, most analysts have adopted the use of this technique in their biological studies and research, which helps them in the determination of any substance found in trace amounts. In addition to the high sensitivity of the fluorimetric technique, it has the advantages of simplicity and being green for the environment. All these reasons encourage the use of fluorimetric spectroscopy for quantifying co-administered therapy in biological fluids, which is considered a crucial step for patients, particularly in emergent cases requiring monitoring of administered therapeutic drugs. In this work, a sensitive, simple, economic, and environmentally friendly fluorimetric analytical technique was developed for the simultaneous determination of prucalopride succinate (a novel anti-constipation agent) and empagliflozin (an anti-diabetic agent) in pharmaceutical forms and spiked plasma depending on third-derivative signal processing at 333 and 314 nm, respectively. Conventional fluorescence spectra of both drugs showed a large overlap that hindered their simultaneous determination. So, third-order derivative fluorescence was adopted to overcome this overlap. The third-derivative corresponding to each spectrum was recorded using data points = 17 and a scaling factor of 10. The greenness of the proposed method was evaluated using an eco-scale scoring system, revealing excellent greenness. Analytical method parameters were validated following ICH guidelines. The method showed high sensitivity, covering a concentration range of 50-1100 ng/mL and 4-500 ng/mL for empagliflozin and prucalopride, respectively, allowing the pharmacokinetic study of both drugs in biological fluids. The LOD values were 14.09 and 0.91 ng/mL, while the LOQ values were 42.72 and 2.77 ng/mL for empagliflozin and prucalopride, respectively.