A step toward simplified detection of serum albumin on SDS-PAGE using an environment-sensitive flavone sensor

Novel photocrosslinking chemical probes utilized for high-resolution spatial transcriptomics

The architecture of cells and the tissue they form within multicellular organisms are highly complex and dynamic. Cells optimize their function within tissue microenvironments by expressing specific subsets of RNAs. Advances in cell tagging methods enable spatial understanding of RNA expression when merged with transcriptomics. However, these techniques are currently limited by the spatial resolution of the tagging, the number of RNAs that can be sequenced, and multiplexing to isolate spatially-distinct cells within the same tissue landscape. To address these limitations, we developed CrossSeq, which employs photocrosslinking fluorescent probes and confocal microscopy activation to demarcate user-defined regions of interest on fixed cells for multiplexed spatial transcriptomic analysis. We investigate phenyl azide and diazirine crosslinking scaffolds and define their photoactivity profiles. We then deploy the aryl azide scaffold with three fluorophores for multiplexing on glyoxal fixed cells and analyze the defined populations using flow cytometry. Finally, we apply CrossSeq to investigate an in vitro MDA-MB-231-LM2 metastatic cancer migration model to evaluate changes in gene expression at the migratory cell front versus the exterior population. We anticipate this new technology will be a valuable tool addition as it will enable easier access to spatial transcriptomic analysis for the scientific community using conventional microscopy and analysis techniques.

Rational design of a dual-mode fluorescent probe for portable detection of pyriproxyfen in the environment and food

The development of a fluorescent probe for pyriproxyfen (PPF) is crucial due to its potential threat to human health. However, the chemical inertness and low solubility of PPF present significant challenges for the detection of PPF in aqueous solutions using fluorescent probes. Herein, we have originally proposed a complex based on 2-(4-(dimethylamino)phenyl)-3-hydroxy-6,7-dimethoxy-4 H-chromen-4-one (HOF) and serum albumin (SA) as a dual-mode fluorescent probe, HOF@SA. This probe utilizes an indicator displacement assay (IDA) to release the dye HOF from the probe at low PPF concentrations (< 10 µM) and embeds the free dye HOF into the micelle of PPF at high concentrations (> 10 µM). This results in dual-mode fluorescent response characteristics for PPF: a turn-off response at low concentrations and a ratiometric response at high concentrations. An investigation of sensing behavior of HOF@SA for PPF detection exhibits rapid response (< 60 s), high sensitivity (LOD ∼4.7 ppb), high selectivity, and excellent visual detection capability (from cyan to yellow). Moreover, with the aid of a portable device, this method enables to analyze PPF in environmental and food samples. These results promote the advancement of a fluorescent probe approach for PPF analysis in environment and food.

NIR-I emissive cyanine derived molecular probe for selective monitoring of hepatic albumin levels during hyperglycemia

In this study, we report a small molecule optical marker BI-CyG derived from the structural engineering of a cyanine scaffold. The developed probe offers suitable advantages over existing cyanine-based albumin specific probes in terms of its excitation and emission wavelengths, which are 760 and 830-832 nm, respectively. Structural tuning of the cyanine architecture leading to extended π-conjugation and resulting in a suitable bathochromic shift in the emission wavelength of the probe is represented in this study. The probe besides emitting in the NIR region, also possesses the desirable characteristics of being a potential target selective optical marker, as established from various biophysical studies. Molecular modelling and simulation studies provided critical insights into the binding of the probe in the protein microenvironment, which was further supported by experimental studies. The probe displayed intracellular albumin selectivity and was utilized for demonstrating alteration in albumin levels in pathological states such as hyperglycemia in hepatic cells. The present study also sheds some light on using BI-CyG as an imaging probe and on the role of metformin as a suitable drug for balancing hyperglycemia-induced reduced intra-hepatic albumin levels. The study, thus, attempts to highlight the structural derivatization of cyanine to afford a potential probe for serum albumin and its deployment to image altering albumin levels in an induced pathological condition, hyperglycemia.

Native mass spectrometry analysis of conjugated HSA and BSA complexes with various flavonoids

Mass spectrometry was used to study the binding interaction between serum albumin proteins (BSA and HSA) and flavone dyes, which is known to induce large fluorescence signals for protein detection. By electrospray ionization mass spectrometry (ESI-MS), multiple charged species/states could be produced in ammonium acetate buffer, while preserving the native structures of the proteins. Subsequent introduction of a flavone dye into the buffered solution resulted in an immediate interaction, forming the respective protein-dye conjugates associated by non-covalent interactions. Formation of protein-dye conjugates induced a notable response in the ESI-MS spectra, including changes in both the charge states and molecular mass of the protein species. The resulting data pointed out that the protein-flavone dye maintained a 1 : 1 ratio in the conjugate, although multiple binding sites for drug molecules are present in albumin proteins.

Rational design of a FA1-targeting anti-interference fluorescent probe for the point-of-care testing of albuminuria

Albuminuria is a crucial urine biomarker of human unhealthy events such as kidney diseases, cardiovascular diseases, and diabetes. However, the accurate diagnosis of albuminuria poses a significant challenge owing to the severe interference from urine fluorescence and urine drugs. Here, we report a novel flavone-based fluorescent probe, DMC, by incorporating the FA1-targeting methylquinazoline group into a flavone skeleton with the extend π-conjugation. DMC exhibited a rapid response time, high sensitivity, and selectivity towards human serum albumin (HSA) in urine. Moreover, the red-shifted fluorescence and the FA1-targeted HSA-binding of DMC efficiently mitigated the interference from both urine fluorescence and urine drug metabolites. Furthermore, the establishment of a portable testing system highlighted the potential for point-of-care testing, offering a user-friendly and accurate approach to diagnose A2-level and A3-level albuminuria. We expect that the success of this DMC-based diagnostic platform in real urine samples can signify a significant advancement in early clinical diagnosis of albuminuria and its associated diseases.

Fluorescent Probes and Quenchers in Studies of Protein Folding and Protein-Lipid Interactions

Fluorescence spectroscopy provides numerous methodological tools for structural and functional studies of biological macromolecules and their complexes. All fluorescence-based approaches require either existence of an intrinsic probe or an introduction of an extrinsic one. Moreover, studies of complex systems often require an additional introduction of a specific quencher molecule acting in combination with a fluorophore to provide structural or thermodynamic information. Here, we review the fundamentals and summarize the latest progress in applications of different classes of fluorescent probes and their specific quenchers, aimed at studies of protein folding and protein-membrane interactions. Specifically, we discuss various environment-sensitive dyes, FRET probes, probes for short-distance measurements, and several probe-quencher pairs for studies of membrane penetration of proteins and peptides. The goals of this review are: (a) to familiarize the readership with the general concept that complex biological systems often require both a probe and a quencher to decipher mechanistic details of functioning and (b) to provide example of the immediate applications of the described methods.

Binding interactions of hydrophobically-modified flavonols with β-glucosidase: fluorescence spectroscopy and molecular modelling study

Natural flavonoids are capable of inhibiting glucosidase activity, so they can be used for treating diabetes mellitus and hypertension. However, molecular-level details of their interactions with glucosidase enzymes remain poorly understood. This paper describes the synthesis and spectral characterization of a series of fluorescent flavonols and their interaction with the β-glucosidase enzyme. To tune flavonol-enzyme interaction modes and affinity, we introduced different polar halogen-containing groups or bulky aromatic/alkyl substituents in the peripheral 2-aryl ring of a flavonol moiety. Using fluorescence spectroscopy methods in combination with molecular docking and molecular dynamics simulations, we examined the binding affinity and identified probe binding patterns, which are critical for steric blockage of the key catalytic residues of the enzyme. Using a fluorescent assay, we demonstrated that the binding of flavonol 2e to β-glucosidase decreased its enzymatic activity up to 3.5 times. In addition, our molecular docking and all-atom molecular dynamics simulations suggest that the probe binding is driven by hydrophobic interactions with aromatic Trp and Tyr residues within the catalytic glycone binding pockets of β-glucosidase. Our study provides a new insight into structure-property relations for flavonol-protein interactions, which govern their enzyme binding, and outlines a framework for a rational design of new flavonol-based potent inhibitors for β-glucosidases.

Screen‐printed electrochemical sensors for label‐free potentiometric and impedimetric detection of human serum albumin

Herein, two electrochemical methods based on potentiometric and impedimetric transductions were presented for albumin targeting, employing screen‐printed platforms (SPEs) to make easy and cost‐effective sensors with good detection merits. The SPEs incorporated ion‐to‐electron multi‐walled carbon nanotubes (MWCNTs) transducer. Sensors were constructed using either tridodecyl methyl‐ammonium chloride (TDMACl) (sensor I) or aliquate 336S (sensor II) in plasticized polymeric matrices of carboxylated poly (vinyl chloride) (PVC‐COOH). Analytical performances of the sensors were evaluated using the above‐mentioned electrochemical techniques. For potentiometric assay, constructed sensors responded to albumin with −81.7 ± 1.7 (r2 = 0.9986) and −146.2 ± 2.3 mV/decade (r2 = 0.9991) slopes over the linearity range 1.5 μM–1.5 mM with 0.8 and 1.0 μM detection limits for respective TDMAC‐ and aliquate‐based sensors. Interference study showed apparent selectivity for both sensors. Impedimetric assays were performed at pH = 7.5 in 10 mM PBS buffer solution with a 0.02 M [Fe(CN)6]−3/−4 redox‐active electrolyte. Sensors achieved detection limits of 4.3 × 10−8 and 1.8 × 10−7 M over the linear ranges of 5.2×10−8–1.0×10−4 M and 1.4×10−6–1.4×10−3 M, with 0.09 ± 0.004 and 0.168 ± 0.009 log Ω/decade slopes for sensors based on TDMAC and aliquate, respectively. These sensors are characterized with simple construction, high sensitivity and selectivity, fast response time, single‐use, and cost‐effectiveness. The methods were successfully applied to albumin assessment in different biological fluids.

A portable paper-based testing device for fast and on-site determination of nitroxynil in food

Nitroxynil (NTX) is a common anthelmintic veterinary drug for the management of fascioliasis in food-producing sheep and cattle. Since excessive NTX residue in food can lead to several adverse side effects, such as allergic skin reaction and respiratory irritation, it is of great importance to develop an efficient analytical method for NTX determination. Herein, we report a simple fluorescent detection method based on a novel supramolecular probe capable of detecting NTX with a fast response (5 s), high sensitivity (107 nM), high selectivity, and acceptable anti-interference property. Moreover, the portable paper-based test strips were facilely prepared and successfully realized on-site determination of NTX in real edible animal products simply with the aid of a smartphone. To the best of our knowledge, this is the very first report on the portable detection of NTX. This study also provides a promising strategy for the fast and portable detection of analyte based on the host-guest system, which will lead to improved fluorescent probe design for food analysis.

Intermolecular proton transfer from flavonol to human serum albumin triggers a red-shifted ratiometric fluorescence response

Intermolecular proton transfer from a flavonol-based probe to the arginine (Arg222) in drug site 1 of human serum albumin triggers an unusual red-shifted ratiometric fluorescence response, which can be applied in the point-to-care diagnosis of hypoalbuminemia.

Surface functionalization of PLGA nanoparticles for potential oral vaccine delivery targeting intestinal immune cells

This study aimed to develop surface modified PLGA nanocarriers protecting a protein-based antigen in the stomach to enable potential release of the antigen at target intestinal sites. PLGA nanoparticles (NPs) were prepared by double emulsion and solvent evaporation techniques while surface functionalization was performed using polyethylene glycol (PEG), sodium alginate (ALG) and Eudragit L100 (EUD) with ovalbumin (OVA) as a model protein antigen. Nanoparticles were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and stability in simulated gastric fluid (SGF)/simulated intestinal fluid (SIF). Structural integrity of released OVA was analyzed by circular dichroism (CD) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), while cytotoxicity against Jurkat cells was determined using MTT assay. Surface functionalized PLGA NPs protected the protein in SGF and SIF better than the non-functionalized NPs. Average size of OVA encapsulated NPs was between 235 and 326 nm and were spherical. FTIR band change was observed after surface modification and the surface modified NPs showed sustained OVA release compared with the uncoated NPs. The secondary structure of OVA released after 96 h remained intact and MTT assay showed >80 % cell viability after 72 h while unmodified and surface modified NPs achieved 17 % and 48 % mucin binding respectively. In conclusion, surface modified PLGA NPs have been shown to be safe for potential oral protein-based vaccine delivery.

Aminoglycoside antibiotic kanamycin functionalized tetraphenylethylene molecular probe for highly selective detection of bovine serum albumin protein

A novel tetraphenylethylene (TPE) functionalized aminoglycoside antibiotic kanamycin (TPE-kana 1) has been successfully synthesized and characterized by means of modern analytical and spectroscopic techniques. The probe TPE-kana 1 showed strong affinity towards bovine serum albumin (BSA) compared to its other biological competitors. The recognition of BSA have been investigated employing UV–Vis absorption and fluorescence emission spectroscopy. The significant color change of TPE-kana 1 with BSA can be observed by necked eye, where the role of AIE-active TPE molecule is handle in both optical and colorimetric changes. The quenching of fluorescence of TPE-kana 1 with BSA was characterized by fluorescence spectroscopy, with 71.16% of quenching efficiency. Moreover, the Stern–Volmer quenching constant was calculated and found to be 2.46 × 10⁷ M⁻¹. Probe TPE-kana 1 showed detection limit of 2.87 nM (nM) towards BSA with binding constant 7.56 × 10⁷ M. A molecular docking study is also performed to investigate the detail interactions between TPE-kana 1 with the sites of BSA via non-covalent i.e., H-bonding, π-cation interactions, π-donor hydrogen bonds and π-π interactions. The lowest binding energy conformation was found at − 10.42 kcal/mol.

General Method for Pesticide Recognition Using Albumin-Based Host-Guest Ensembles

The massive use of pesticides nowadays has led to serious consequences for the environment and public health. Fluorescence analytical methods for pesticides are particularly advantageous with respect to simplicity and portability; however, currently available fluorescence methods (enzyme-based assays and indicator displacement assays) with poor universality are only able to detect few specific pesticides (e.g., organophosphorus). Making use of the multiple flexible and asymmetrical binding sites in albumin, we herein report a set of multicolor albumin-based host-guest ensembles. These ensembles exhibit a universal but distinctive fluorescent response to most of the common pesticides and allow array-based identification of pesticides with high accuracy. Furthermore, the simplicity, portability, and visualization of this method enable on-site determination of pesticides in a practical setting. This albumin host strategy largely expands the toolbox of traditional indicator displacement assays (synthetic macrocycles as hosts), and we expect it to inspire a series of sensor designs for pesticide detection.

A near-infrared dicyanoisophorone-based fluorescent probe for discriminating HSA from BSA

Despite the rapid development of fluorescent probe techniques for the detection of human serum albumin (HSA), a probe that discriminates between HSA and bovine serum albumin (BSA) is still a challenging task, since their similar chemical structures. As a continuation of our work, herein, a dicyanoisophorone-based fluorescent probe DCO2 is systematically studied for discrimination of HSA from BSA. The photophysical and sensing performances of DCO2, including basic spectroscopic properties, sensing sensitivity, and selectivity, exhibits that DCO2 could selectively bind with HSA and display remarkable fluorescence enhancement (∼254-fold) at 685 nm. The gap of the fluorescent response of DCO2 between HSA and BSA is an obvious increase from 21% to 73% compared to the previous probe DCO1. The sensing mechanism was elucidated by Job's plot, displacement experiment, and molecular docking, suggesting that the specific response to HSA originated from the rigid donor structure and steric hindrance. DCO2 could be buried in the DS1 pocket of HSA, and only partly wedged into the DS1 pocket of BSA with exposing twisted N,N-diethylamino group outside. Application studies indicated that DCO2 has well detective behavior for HSA in the biological fluids. This work could provide a new approach to design HSA-specific near-infrared fluorescence probes.

Near-infrared emissive cyanine probes for selective visualization of the physiological and pathophysiological modulation of albumin levels

With the promising advantages of the near-infrared region (NIR) emissive markers for serum albumin becoming very prominent recently, we devised CyG-NHS as the cyanine derived longest NIR-I emissive optical marker possessing albumin selective recognition ability in diverse biological milieu. Multiscale modeling involving molecular docking, molecular dynamics, and implicit solvent binding free energy calculations have been employed to gain insights into the unique binding ability of the developed probe at domain-I of albumin, in contrast to the good number of domain IIA or IIIA binding probes available in the literature reports. The binding free energy was found to be -31.8 kcal mol^-1 majorly predominated by hydrophobic interactions. Besides, the conformational dynamics of CyG-NHS in an aqueous medium and the albumin microenvironment have been comprehensively studied and discussed. The potentiality of this optical platform to monitor the intracellular albumin levels in human hepatoma (HepG2) cells in different pathophysiological states has been demonstrated here. Also, the competency of the phenformin drug in restoring the albumin levels in chronic hyperinsulinemic and hypercholesterolemic in vitro models has been established through the visualization approach. Altogether, the findings of this study throw light on the significance of the development of a suitable optical marker for the visualization of critical bioevents related to albumin.

Modulating donor of dicyanoisophorone-based fluorophores to detect human serum albumin with NIR fluorescence

It is urgently needed to develop NIR-fluorescent probe for detection of human serum albumin (HSA) since the interference of short-wavelength-fluorescence from endogenous species in real serum and urine. However, most previous reports were located in the short-wavelength region (<600 nm). In this work, a series of dicyanoisophorone (DCO)-based fluorophores 1-4 with different donor groups have been designed and investigated. A systematic study of their photophysical properties has been carried out. Among these probes, 4 exhibited NIR emission with the highest fluorescence brightness and the most sensitive signal response to HSA. Further studies demonstrated that 4 could strongly bind into the DS1 pocket of HSA with a 1:1 ratio. Importantly, the method based on 4 has been proven to be capable of sensing HSA in real serum and urine samples.

Enhancing Stability and Mucoadhesive Properties of Chitosan Nanoparticles by Surface Modification with Sodium Alginate and Polyethylene Glycol for Potential Oral Mucosa Vaccine Delivery

Background: The present study aimed to fabricate surface-modified chitosan nanoparticles with two mucoadhesive polymers (sodium alginate and polyethylene glycol) to optimize their protein encapsulation efficiency, improve their mucoadhesion properties, and increase their stability in biological fluids. Method: Ionotropic gelation was employed to formulate chitosan nanoparticles and surface modification was performed at five different concentrations (0.05, 0.1, 0.2, 0.3, 0.4% w/v) of sodium alginate (ALG) and polyethylene glycol (PEG), with ovalbumin (OVA) used as a model protein antigen. The functional characteristics were examined by dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM)/scanning transmission electron microscopy (STEM). Stability was examined in the presence of simulated gastric and intestinal fluids, while mucoadhesive properties were evaluated by in vitro mucin binding and ex vivo adhesion on pig oral mucosa tissue. The impact of the formulation and dissolution process on the OVA structure was investigated by sodium dodecyl-polyacrylamide gel electrophoresis (SDS-PAGE) and circular dichroism (CD). Results: The nanoparticles showed a uniform spherical morphology with a maximum protein encapsulation efficiency of 81%, size after OVA loading of between 200 and 400 nm and zeta potential from 10 to 29 mV. An in vitro drug release study suggested successful nanoparticle surface modification by ALG and PEG, showing gastric fluid stability (4 h) and a 96 h sustained OVA release in intestinal fluid, with the nanoparticles maintaining their conformational stability (SDS-PAGE and CD analyses) after release in the intestinal fluid. An in vitro mucin binding study indicated a significant increase in mucin binding from 41 to 63% in ALG-modified nanoparticles and a 27–49% increase in PEG-modified nanoparticles. The ex vivo mucoadhesion showed that the powdered particles adhered to the pig oral mucosa. Conclusion: The ALG and PEG surface modification of chitosan nanoparticles improved the particle stability in both simulated gastric and intestinal fluids and improved the mucoadhesive properties, therefore constituting a potential nanocarrier platform for mucosal protein vaccine delivery.

Flavonol-Based Carbon Monoxide Delivery Molecule with Endoplasmic Reticulum, Mitochondria, And Lysosome Localization

Light-triggered carbon monoxide (CO) delivery molecules are of significant current interest for evaluating the role of CO in biology and as potential therapeutics. Herein we report the first example of a metal free CO delivery molecule that can be tracked via confocal microscopy at low micromolar concentrations in cells prior to CO release. The NEt₂-appended extended flavonol (4) localizes to the endoplasmic reticulum, mitochondria, and lysosomes. Subcellular localization of 4 results in CO-induced toxicity effects that are distinct as compared to a nonlocalized analog. Anti-inflammatory effects of 4, as measured by TNF-α suppression, occur at the nanomolar level in the absence of CO release, and are enhanced with visible-light-induced CO release. Overall, the highly trackable nature of 4 enables studies of the biological effects of both a localized flavonol and CO release at low micromolar to nanomolar concentrations.

Fluorescence discrimination of HSA from BSA: A close look at the albumin-induced restricted intramolecular rotation of flavonoid probe

Discrimination of human serum albumin (HSA) from bovine serum albumin (BSA) based on the fluorescence probe technique is still challenging due to similar chemical structures. In this work, a novel flavonoid-based fluorescent probe AF is reported for successful discrimination of HSA from BSA. The sensing performances of probe, including sensing dynamic, sensitivity and selectivity, have been carefully studied. Moreover, sensing mechanism was elucidated by Job's plot, displacement experiment, and molecular docking, suggesting that the specific response to HSA originated from the albumin-induced restricted intramolecular rotation (RIR) of probe. This work may provide a simple way for designing of novel probes for HSA with high selectivity.

Computational Calculation of Dissolved Organic Matter Absorption Spectra

The absorption spectrum of dissolved organic matter (DOM) is a topic of interest to environmental scientists and engineers as it can be used to assess both the concentration and physicochemical properties of DOM. In this study, the UV-vis spectra for DOM model compounds were calculated using time-dependent density functional theory. Summing these individual spectra, it was possible to re-create the observed exponential shape of the DOM absorption spectra. Additionally, by predicting the effects of sodium borohydride reduction on the model compounds and then calculating the UV-vis absorbance spectra of the reduced compounds, it was also possible to correctly predict the effects of borohydride reduction on DOM absorbance spectra with a relatively larger decrease in absorbance at longer wavelengths. The contribution of charge-transfer (CT) interactions to DOM absorption was also evaluated, and the calculations showed that intra-molecular CT interactions could take place, while inter-molecular CT interactions were proposed to be less likely to contribute.

About the mechanism of ultrasonically induced protein capsule formation

In this paper, we propose a consistent mechanism of protein microcapsule formation upon ultrasound treatment. Aqueous suspensions of bovine serum albumin (BSA) microcapsules filled with toluene are prepared by use of high-intensity ultrasound following a reported method. Stabilization of the oil-in-water emulsion by the adsorption of the protein molecules at the interface of the emulsion droplets is accompanied by the creation of the cross-linked capsule shell due to formation of intermolecular disulfide bonds caused by highly reactive species like superoxide radicals generated sonochemically. The evidence for this mechanism, which until now remained elusive and was not proven properly, is presented based on experimental data from SDS-PAGE, Raman spectroscopy and dynamic light scattering.

A DS2-specific flavonoid-based probe with a unique dual-emissive response to human serum albumin

The hydroxyl substituent in flavonoids can cause the binding site to change from DS1 to DS2 and restore the ESIPT process of flavonoids, thereby leading to a unique dual-emissive response towards human serum albumin.

Pseudosterase activity-based specific detection of human serum albumin on gel

Human serum albumin (HSA) has pseudoesterase activity. So far on gel specific detection of such property of HSA is never reported. Moreover, protein binding dyes are non-specific for albumin. However, many of such dyes are used for HSA detection. So, dye-based albumin detection on the gel is expected to generate false-positive results for HSA. In this context, we have discovered that Fast Blue BB (FBBB, 0.12%) stains specifically HSA pseudoesterase activity with 2 Naphthyl acetate (2NA) as an ester substrate. Further, neostigmine has not inhibited the pseudoesterase activity associated with HSA. Neostigmine is a known inhibitor of many true esterases like acetylcholinesterase. So, neostigmine addition offers specificity to the method developed for staining of HSA. Additionally, 2NA stains HSA better than bovine serum albumin (BSA). Exploring all these novel findings, we have devised a simple method of HSA detection on the gel, accurately where other esterases are not detected. To the best of our knowledge, our method is the first to detect HSA pseudoesterase activity specifically on gel without getting interfered by any other esterase activity. The method detects HSA better than BSA. We feel that this method will go a long way for the specific detection of HSA on the gel. It is also relevant for understanding the purity of donor human milk matrix and pharmaceutical preparation of HSA. Our method can detect 7 μM of added HSA in human urine. Therefore, our method can be proceeded further for microalbuminuria detection in days to come.

Interaction of flavonoids with serum albumin: A review

Flavonoids are plant products abundant in every day diet and claimed to be beneficial for human health. After absorption, flavonoids are transported by the serum albumin (SA), the most abundant carrier blood protein, through formation of flavonoids-SA complex. This review deals with the current state of knowledge on flavonoids-SA complex over the past 10 years, mainly involved multi-spectroscopic techniques and molecular dynamics simulation studies to explore the binding mechanism, thermodynamics and structural aspects of flavonoids binding to SA. Especially, the novel method, capillary electrophoresis, high performance affinity chromatography approach, native mass spectrometry and microscale thermophoresis used in characterization of the interaction between flavonoids and SA as well as flavonoid-based fluorescent probe for SA measurement are also included in this review.

Synthesis of a far-red emitting flavonoid-based lysosome marker for live cell imaging applications

A bright far-red emitting flavonoid derivative (FuraET) was synthesized in good yields by inserting a π extension group (i.e., furan) into the flavonoid skeleton, via using the Suzuki-Miyaura cross-coupling reaction. FuaraET exhibited optical absorption at λ_ab ≈ 450 nm and emission λ_em ≈ 660 nm by recognizing as the first far-red emitting flavonoid derivative reported. FuraET exhibited a large Stokes shift (Δλ > 150 nm) high fluorescent quantum yield (φ_fl ≈ 0.2-0.4), and good photostability indicating excellent characteristics for an imaging probe. Live cell fluorescent confocal microscopy imaging revealed the exceptional selectivity of the FuraET towards cellular lysosomes (Mander's overlap coefficients >0.9). The observed non-alkalinizing nature and high biocompatibility (LC₅₀ > 50 µM) suggested that FuraET can a reliable lysosome marker for live cell imaging experiments. Our further study also indicated that FuraET may likely internalized into hydrophobic regions of the cellular lysosomes in contrast to acidic lysosomal lumen.

Deciphering the positional impact of chlorine in a new series of berberine analogues towards the superb-selective “turn-on” hydrophobic signaling of bovine serum albumin at physiological pH

We report a new 9-O-benzyl substituted berberine analogue for the selective detection of BSA with a limit of detection value of 3.30 nM.

Molecular Scale Optimum Hydrophobicity To Establish an Enhanced Probe-Protein Interaction: Near-Infrared Imaging of Albumin Biosynthesis Modulation

Albumin is the most abundant serum protein and shows variation in its synthesis rate in different physiological and pathophysiological conditions. Thus, there might be an association expected between serum albumin concentration and body health. A library of NIR probes engineered with the optimum hydrophobicity has been developed and characterized using spectroscopy techniques and was employed to understand the variation of hepatic albumin synthesis rates on physiological and pathophysiological states. Given the importance of hydrophobicity in rendering an effective interaction of small molecules with biomolecules, strategic structure interaction relationship studies led us toward the development of a potent emissive molecular probe through chemical library development. By exploration of these newly developed molecular probes, our study elegantly showed how a pathophysiological condition like the hyperinsulinemic state significantly downregulates albumin biosynthesis in HepG2 cells using fluorescence microscopy as a tool. An excellent correlation between the albumin transcript level and fluorescence intensity inside the cells has been observed. The key role of hydrophobicity resulting in an effective interaction of the probes with albumin, thus leading to strong optical signals, has been experimentally demonstrated in this report. Also, a siRNA interference technique has been utilized to establish the excellent selectivity of the developed probes with excitation as well as emission in the NIR region. We therefore have established through our experimental findings that suitable cell permeable emissive molecular markers with a high degree of albumin specificity can be used as a good optical tool for studying the effect of hyperinsulinemia on albumin biosynthesis modulation.

A flavonoid-based fluorescent probe enables the accurate quantification of human serum albumin by minimizing the interference from blood lipids

We herein provide a simple design strategy to improve the sensing specificity towards human serum albumin by incorporating a nitrobenzene quencher into a traditional polarity-sensitive probe in responding to the interference from blood lipids.

A bright red-emitting flavonoid for Al3+ detection in live cells without quenching ICT fluorescence

A bright red-emitting flavonoid derivative was synthesized, which exhibited a large Stokes shift (Δλ > 150 nm) and high fluorescence quantum yields (ϕ_fl = 0.10–0.35).

A fluorescent flavonoid for lysosome detection in live cells under "wash free" conditions

Lysosomes are vital organelles in living cells, which have acidic environments (pH 4.0-5.0) where macrobiomolecules and malfunctioning organelles are broken down into monomers by hydrolase activity. The majority of the currently reported fluorescent probes for detecting lysosomes suffer from small Stokes shifts (Δλ < 20 nm) and higher cytotoxicity due to an "alkalinizing effect". An interesting flavonoid-based lysosome probe is synthesized by introducing a morpholine moiety onto the flavonoid skeleton. This new probe has shown excellent selectivity to detect lysosomes in MO3.13 oligodendrocytes and normal human lung fibroblast cell lines. Probes 1a and 1b have shown excellent fluorescence quantum yield (φ_fl up to 0.43 in non-aqueous solvents) and large Stokes shifts (120-150 nm). These new fluorescent probes also exhibit a large quantum yield difference from an aqueous to organic environment, making them potentially useful as "wash-free" stains for visualizing lysosomes. Cell viability evaluation of these probes shows excellent biocompatibility with the median lethal concentration being LC50 ≈ 50 μM.

Curcumin encapsulated zeolitic imidazolate frameworks as stimuli responsive drug delivery system and their interaction with biomimetic environment

Metal organic frameworks (MOFs) exhibit unique features of finely tunable pore structures, excellent chemical stability and flexible surface structural functionality, making them advantageous for a wide range of applications including energy storage, compound separation, catalysis, and drug delivery. The present work enlightens a novel approach of single step fabrication of CCM-ZIF-8 as a drug carrier and its application as stimuli responsive drug delivery systems via external stimuli involving change in pH and in presence of biomimetic cell membrane like environment using liposomes and SDS micelles. The methodology is devoid of any post synthesis drug loading steps. The synthesized curcumin encapsulated ZIF-8 frameworks demonstrate ultrahigh drug encapsulation efficiency (ca. 83.33%) and good chemical stability. In vitro drug release of curcumin was three times higher in acidic medium than in physiological pH. Cytotoxicity results demonstrated enhanced therapeutic effect of CCM-ZIF-8 than free curcumin. Confocal microscopy results confirmed the easy cellular internalization of CCM-ZIF-8 in HeLa cells. Intracellular distribution studies at various incubation times confirmed the clathrin-mediated endocytosis to lysosomal pathway of CCM-ZIF-8, but without mitochondria being an intracellular fate. The results signify that CCM-ZIF-8 is an efficient drug carrier for passive tumor therapy in future for cancer treatments.

A fluorescence turn-on probe for human (bovine) serum albumin based on the hydrolysis of a dioxaborine group promoted by proteins

A reaction-based florescence probe CBF for serum albumin (SA) was proposed by connecting a dioxaborine unit with environment-sensitive coumarin fluorophore. CBF exhibits high selectivity and sensitivity toward SA over other biologically relevant species and has potential of detecting SA in biosamples.

Properties of a flavonol-based photoCORM in aqueous buffered solutions: influence of metal ions, surfactants and proteins on visible light-induced CO release

A flavonol-based photoCORM exhibits reliable visible light-induced CO release in aqueous buffer environments containing constituents of relevance to biological environments.

Fluorescence detection of endogenous bisulfite in liver cancer cells using an effective ESIPT enhanced FRET platform

Probe L-HF1, which featured large (pseudo) Stokes shifts and high FRET efficiency, was designed on a new ESIPT enhanced FRET platform for the detection of HSO₃⁻/SO₃²⁻.

Solvatochromic fluorescent probes for recognition of human serum albumin in aqueous solution: Insights into structure-property relationship

Human serum albumin (HSA) as the most abundant protein in human blood plasma, serves many physiological functions. The dysregulation of HSA in serum or in urine is associated with various diseases, such as cirrhosis of liver, multiple myeloma, and cardiovascular disease. Therefore, to quantify HSA in body fluids with high selectivity and sensitivity is of great significance for disease diagnosis and preventive medicine. We herein developed a series of amide-functionalized flavonoids probes, 1-3, for recognition of human serum albumin. All flavonoids could be easily prepared by a Claisen-Schmidt condensation and Algar-Flynn-Oyamada reaction, and showed positive solvatochromism on their dual emissions. The chemical structure of flavonoids played an important role on their HSA-sensing abilities. Among three probes, the compound 1 showed the highest sensitivity, the remarkable selectivity, and the quantitive response for HSA in aqueous solution. Together with its high tolerance of environmental pH, anti-interference properties, and time-insensitivity, thus it provides a promising sensing method for HSA.

Fluorescent flavonoids for endoplasmic reticulum cell imaging

Visualization of subcellular organelles in vivo is critical for basic biomedical research and clinical applications. Two new flavonoids with an amide substituent were synthesized and characterized. The flavonoids were nearly non-fluorescent in aqueous environment, but exhibited two emission peaks (one λ_em at 495-536 nm and the other at 570-587 nm) in organic solvents, which were assigned to the excited normal (N^*) and tautomer (T^*) emission. When the dyes were examined on oligodendrocyte cells, they were found to selectively accumulate in the endoplasmic reticulum (ER), a eukaryotic organelle involved in lipid and protein synthesis, giving fluorescence turn-on. The ER-selective flavonoids could be a valuable tool due to its low molecular mass (<500), large Stokes' shift, low toxicity, and biocompatibility.