Enhanced fluorescent iron oxide quantum dots for rapid and interference free recognizing lysine in dairy products

Novel blue-pea flowers derived-carbon dots/iron oxide nanohybrid as sustainable "turn-off" fluorescent nanosensor for selective Fe3+ detection in food samples

Developing a novel fluorescence carbon-based sensor with high sensitivity, selectivity, and rapid response is critical for detecting ferric ion (Fe3+) in beverages and food products. Overcoming this challenge is essential, as excess Fe3+ can cause cellular damage, raising health concerns. Herein, we designed a fluorescence nanosensor utilizing a hybrid iron oxide/carbon dots (HICs) nanocomposite, synthesized from blue pea (BPs) flowers and iron oxide nanoparticles through a hydrothermal treatment. More importantly, the HICs demonstrated high sensitivity and a rapid response to Fe3+, with a linear detection range spanning 0.06 to 100 µM and an impressively low limit of detection (LOD) of 13.61 nM. Moreover, the HICs exhibited remarkable selectivity toward Fe3+, remaining unaffected by various interferences, including common metal ions and small organic molecules. Upon Fe3+ addition, the fluorescence quenching of HICs occurs through a combination of static quenching and dynamic quenching mechanism and the inner filter effect. Additionally, the detection of Fe3+ in milk and herbal drinks was achieved using HICs, yielding satisfactory recovery rates ranging from 94.4 % to 103.7 %. Thus, the developed HICs serve as highly efficient "turn-off'" fluorescent nanosensors, exhibiting a rapid response, high sensitivity, and ultra-selectivity for Fe3+ detection, unaffected by matrix interference. These qualities make them promising candidates for advanced detection applications in food products, ensuring food safety.

A "turn-on" fluorescence polyethyleneimine-based nanosensor chemosensor for sensing of l-lysine

A novel polymeric nanosensor (named PEINAC) based on polyethyleneimine (PEI), was designed for the selective fluorescence detection of l-lysine (L-Lys) in aqueous solutions. The sensor was synthesized through a one-step, three-component reaction involving orthophthalaldehyde (OPA), PEI, and acetylcysteine. This reaction simultaneously facilitated the creation of an isoindole fluorophore, which was chemically attached to the PEI backbone. The structural properties, size, and morphology of PEINAC were thoroughly analyzed using various characterization techniques. When introduced into a buffered solution at pH 7.0, PEINAC demonstrated high specificity for L-Lys, inducing a marked fluorescence enhancement at 450 nm upon excitation at 367 nm. The fluorescence intensity exhibited a linear relationship with L-Lys concentration, ranging from 1 μM to 1000 μM, with a detection limit of 0.13 μM. Notably, the sensor exhibited excellent selectivity, showing no significant interference from other biomolecules and common transition metal ions and anions. This sensor was successfully applied for L-Lys quantification in blood and urine samples and for cellular L-Lys imaging, demonstrating its potential in various analytical and biomedical applications.

Lysine enhances the photoresponsive oxidase-like activity of twin Cd0.7Zn0.3S for direct colorimetric detection of lysine

BACKGROUND

Lysine (Lys) is one of the eight essential amino acids for the human body, which can't be synthesized by the body and must be obtained from external sources. And the detection of Lys is of significance for disease monitoring. The construction of photoresponsive nanozymes based analytical methods have received increasing attention and have been successfully achieved for the detection of metal ions, small molecules and natural enzymes. However, the exploration of photoresponsive nanozyme in amino acids detection has not been tapped.

RESULTS

This study presents an innovative method based on surface passivation by Lys to stimulate the photoresponsive nanozyme activity of twin Cd0.7Zn0.3S nanomaterials. Specifically, Lys can bind with twin Cd0.7Zn0.3S, which filled the dangling bonds on the surface of Cd0.7Zn0.3S and caused passivation of the surface state, resulting in the promotion of the separation efficiency of electrons and holes, along with the facilitation of the production of active intermediates. Therefore, the Cd0.7Zn0.3S in the presence of Lys showed a high catalytic oxidation ability for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to oxidized TMB (oxTMB). This new kind of photoresponsive oxidase-like activity could be regulated by switching visible light sources and showed the specificity of being only affected by Lys without influenced by other amino acids, thus achieved direct colorimetric detection of Lys. The linear range for Lys detection was 1-100 μM, with a detection limit of 0.18 μM (S/N = 3).

SIGNIFICANCE

This study developed a new nanozyme of twin Cd0.7Zn0.3S, whose activity leverages on Lys as a stimulator. Moreover, the Lys detection method proposed by us had the characteristics of high sensitivity, good selectivity, fast detection speed, and low cost. Therefore, it holds significant potential application value, making it a promising candidate in the field of Lys detection and related research areas.

A novel boronic acid-based fluorescent sensor for the selective detection of l-lysine in food samples and cells

A novel probe DFC (2-(dicyanomethylene)-2,5-dihydro-5,5-dimethyl-4-((E)-2-(5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)furan-2-yl)vinyl)furan-3-carbonitrile) was successfully designed and synthesized for the detection of l-lysine (l-Lys). The sensing behavior was characterized using absorption and fluorescence emission spectra. Upon addition of l-Lys to DFC, a rapid response time of 5 seconds was observed, accompanied by a significant 4-fold enhancement in fluorescence intensity. Additionally, DFC exhibits an impressively low detection limit of 0.14 μMol L-1. Furthermore, the applicability of DFC was demonstrated through successful detection of l-Lys in water samples, food samples, and imaging of l-lys in live HeLa cells.

An octahedral metal oxide nanoparticle-based dual-signal sensing platform for simultaneous detection of histidine and lysine in human blood plasma and urine

Histidine and lysine serve as essential amino acids in physiological processes and biomarkers for specific diseases, requiring precise detection methods in a variety of samples. This study presents an affordable single colorimetric probe that employs nickel oxide nanoparticles (NiONPs) as an artificial enzyme to detect histidine and lysine, improving conventional analytical limitations. The characterization of NiONPs was executed using SEM-EDX, FE-SEM, FTIR and XRD. The NiONPs demonstrated peroxidase-like catalytic activity on the conversion of TMB to oxidized TMB (oxTMB) in the presence of H2O2, utilizing optimization parameters like pH value (3), TMB concentration (10 mM), H2O2 concentration (60 mM), and incubation time (18 min). The study revealed that Ni and O atoms are present on the surface of NiONPs, allowing for specific interactions with essential amino acids and temporarily hindering the catalytic activity of oxidized TMB. The method exhibited a low limit of detection (LOD) of 0.07 μM (10-100 μM) for histidine and 1.1 μM (15-150 μM) for lysine with good stability. The proposed strategy was validated with urine and plasma samples, yielding favorable recoveries of 93.6-98.2% in urine and 90.5-96.0% in plasma for histidine and 91.2-94.8% in urine and 88.4-93.3% in plasma for lysine, supporting its selectivity, feasibility, and reliability for practical applications. In the future, this methodology will facilitate the integration of histidine and lysine detection into microfluidic systems using NiONPs as a colorimetric probe.

Colorimetric and Smartphone-Based Dual-Mode Rapid Detection of Congo Red Using Iron Oxide Quantum Dots

Congo red is toxic to humans and the environment and persists in the environment for long periods. Therefore, developing a rapid detection method for Congo red is crucial. In this study, iron oxide quantum dots (IOQDs) were synthesized and employed for dual-mode detection (colorimetric and smartphone-based) of Congo red in real samples. Upon mixing with Congo red, the IOQDs induce a color change in the solution due to the strong intermolecular interactions between Congo red and the IOQDs, making them practical as colorimetric sensors. To further increase the on-site detection capabilities of IOQDs, images of the sensor platform were captured using a smartphone, and the color data were analyzed with a dedicated APP. As a colorimetric sensor, the ultraviolet-visible (UV-vis) absorbance response exhibited good linearity for Congo red concentrations between 2 and 50 μM, with a detection limit of 0.89 μM. The smartphone-based sensor also provided highly quantitative results, showing a linear relationship between Congo red concentrations and the blue-to-red (B/R) channel ratio, with a detection limit of 0.58 μM. Moreover, this dual-mode method demonstrated better selectivity for Congo red than other colorimetric sensors, even in the presence of other red dyes. The proposed method is convenient, fast, low-cost, and suitable for real-sample applications.

Fluorescence and Colorimetric Dual-Readout Detection of Tetracycline Using Leucine-Conjugated Iron Oxide Quantum Dots

This study developed a dual-readout system utilizing fluorescence and colorimetry based on iron oxide quantum dots (IO-QDs) for detecting tetracycline (TCy). IO-QDs were synthesized within 6 h using L-leucine as a surface modifier, achieving a more efficient route. Upon interaction with TCy, IO-QDs exhibited a significant decrease in fluorescence response and observable color changes, while fluorescence lifetime remained consistent regardless of TCy presence. Moreover, IO-QDs' fluorescence response remained stable across various temperatures. The Förster resonance energy transfer distance of less than 2 nm and a quenching constant of 2.90 × 1012 M-1s-1 indicated static quenching in the presence of TCy. Additionally, significant changes in observed and corrected fluorescence efficiency suggested the involvement of the inner filter effect in the fluorescence quenching of IO-QDs. The synthesized IO-QDs were then utilized for selective and rapid fluorescence-based TCy detection, showing a linear range of 0.5 to 80 μM. Simultaneously, a colorimetric method for TCy detection was established, demonstrating a good linear relationship within the range of 0.5 to 20 μM. The detection limits for TCy were determined as 0.539 and 0.329 μM using fluorescence and colorimetric approaches, respectively. Furthermore, IO-QDs were applied to detect real samples, and the dual-readout probe exhibited satisfactory recoveries, confirming the practical reliability of the developed method for analyzing milk and drinking water samples.

Near-infrared fluorescent probe with large Stokes shift for specific detection of lysine

A new near-infrared (NIR) fluorescent probe CL based on coumarin- dicyanoisophorone was synthesized. Addition of Lys to probe CL solution in DMF/H2O (9:1, v/v) medium resulted in noticeable enhancement in the intensity of the fluorescence emission at 702 nm, accompanying distinct color change from yellow to pink. While addition of other amino acids and biothiols (Gly, Hcy, GSH, Glu, Val, Tyr, Arg, Trp, Lys, His, Leu, Phe, Asp and Met) did not bring about substantial changes in both fluorescence emission and color. The detection limit was calculated to be 0.51 μM. Job's plot test revealed that probe CL and Lys formed a complex of 1:1 stoichiometry. Probe CL showed high stability and could be used to recognize Lys in a wide pH range of 4.0-10.0. The sensing mechanism was proposed and verified by 1H NMR spectral measurement. The dual-modal fluorescence turn-on and colorimetric NIR probe with an extremely large Stokes shift of 280 nm may be utilized for highly specific and practical sensing of Lys.

Turn-off/turn-on biosensing of tetracycline and ciprofloxacin antibiotics using fluorescent iron oxide quantum dots

A fluorescence probe based on iron oxide quantum dots (IO-QDs) was synthesized using the hydrothermal method for the determination of tetracycline (TCy) and ciprofloxacin (CPx) in aqueous solution. The IO-QDs were characterized using high-resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), vibrating sample magnetometry (VSM), and Fourier-transform infrared spectroscopy (FTIR). The as-prepared IO-QDs are fluorescent, stable, and with a fluorescence quantum yield (QY) of 9.8 ± 0.12%. The fluorescence of IO-QDs was observed to be quenched and enhanced in the presence of TCy and CPx, respectively. The fluorescence intensity ratio shows linearity at concentrations from 1-100 μM and 5-100 μM for TCy and CPx, respectively; the detection limit for TCy and CPx was estimated to be 0.71 μM and 1.56 μM, respectively. The proposed method was also successfully utilized in the spiked samples of drinking water and honey with good recoveries. The method offered convenience, rapid detection, high sensitivity, selectivity, and cost-efficient alternative options for the determination of TCy and CPx in real samples.

Glutamic acid-capped iron oxide quantum dots as fluorescent nanoprobe for tetracycline in urine

The fabrication of iron oxide quantum dots (IO-QDs) modified with glutamic acid (Glu) under controllable conditions is reported. The IO-QDs have been characterized by transmission electron microscopy, spectrofluorometry, powder X-ray diffraction, vibrating sample magnetometry, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The IO-QDs exhibited good stability towards irradiation, temperature elevations, and ionic strength, and the quantum yield (QY) of IO-QDs was calculated to be 11.91 ± 0.09%. The IO-QDs were furtherly measured at an excitation wavelength of 330 nm with emission maxima at 402 nm, which were employed to detect tetracycline (TCy) antibiotics, including tetracycline (TCy), chlortetracycline (CTCy), demeclocycline (DmCy), and oxytetracycline (OTCy) in biological samples. The results indicated that TCy, CTCy, DmCy, and OTCy in urine samples show a dynamic working range between 0.01 and 80.0 μM; 0.01 and 1.0 μM; 0.01 and 10 μM; and 0.04 and 1.0 μM, respectively, with detection limits of 7.69 nM, 120.23 nM, 18.20 nM, and 67.74 nM, respectively. The detection was not interfered with by the auto-fluorescence from the matrices. In addition, the obtained recovery in real urine samples suggested that the developed method could be used in practical applications. Therefore, the current study has prospect to develop an easy, fast, eco-friendly, and efficient new sensing method for detecting tetracycline antibiotics in biological samples.

Amorphous Ultra-Small Fe-Based Nanocluster Engineered and ICG Loaded Organo-Mesoporous Silica for GSH Depletion and Photothermal-Chemodynamic Synergistic Therapy

Intracellular oxidative amplification can effectively destroy tumor cells. Additionally, Fe-mediated Fenton reaction often converts cytoplasm H2 O2 to generate extensive hypertoxic hydroxyl radical (• OH), leading to irreversible mitochondrion damage for tumor celleradication, which is widely famous as tumor chemodynamic therapy (CDT). Unfortunately, intracellular overexpressed glutathione (GSH) always efficiently scavenges • OH, resulting in the significantly reduced CDT effect. To overcome this shortcoming and improve the oxidative stress in cytoplasm, Fe3 O4 ultrasmall nanoparticle encapsulated and ICG loaded organo-mesoporous silica nanovehicles (omSN@Fe-ICG) are constructed to perform both photothermal and GSH depletion to enhance the Fenton-like CDT, by realizing intracellular oxidative stress amplification. After this nanoagents are internalized, the tetrasulfide bonds in the dendritic mesoporous framework can be decomposed with GSH to amplify the toxic ROS neration by selectively converting H2 O2 to hydroxyl radicals through the released Fe-based nanogranules. Furthermore, the NIR laser-induced hyperthermia can further improve the Fenton reaction rate that simultaneously destroyed the mitochondria. As a result, the GSH depletion and photothermal assisted CDT can remarkably improve the tumor eradication efficacy.