A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone

The FRET-Based APTA Sensor/Cy3 Complex for Glucose Determination

This study developed a sensitive and cost-effective fluorescent probe based on the Förster Resonance Energy Transfer (FRET) method to monitor blood glucose levels. The APTA sensor/Cy3 probe consisted of cadmium telluride quantum dots modified with thioglycolic acid (CdTe-TGA QDs), a thiol-glucose-aptamer, and a Cy3-labeled aptamer. Due to the well-matched emission spectrum of the CdTe QDs and the absorption spectrum of Cy3, the FRET system decreased fluorescence intensity. However, glucose molecules quenched it when introduced to the system. The linear relationship between fluorescence intensity and glucose concentration was established with a detection limit of 7.72 × 10-9 M. The APTA sensor/Cy3 complex demonstrated excellent selectivity and specificity toward glucose and a high recovery rate of 96.00-101.11% in human serum and urine using the spiking method. The structural and morphological characteristics of the APTA sensor/Cy3 complex were confirmed by UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS) analyses. The results suggest that the FRET-based APTA sensor/Cy3 complex would lead to the development of fluorescent probes for screening biological metabolites in clinical diagnostics and research.

Rationally design a novel Zn-MOF for fluorescent detection of nitrofuran antibiotics: The synthesis, structure and sensing applications

Nitrofuran antibiotics (NFAs) residues in waterare a persistent concern for the public due to the potential threats they pose to human health and the environment. Therefore, efficient probes that are capable of detecting trace amounts of antibiotics in real water environments have become a top priority. Herein, a novel fluorescent Zn-MOF probe (MOF-1) was revealed for the highly selective and sensitive sensing of NFAs. MOF-1 was rationally constructed with Zn(NO3)2·6H2O, 5,5'-(anthracene-9,10-diyl) diisophthalic acid (H4ADIP) and 1,3-bis(imidazol-1-ylmethyl)-benzene (mbib) by using the solvothermal method. Fluorescence sensing experiments demonstrate that MOF-1 can function as a fluorescent sensor for selective, sensitive, and rapid detection of NFAs among 15 antibiotics including ciprofloxacin (CPFX), chloramphenicol (CAP), sulfonamides and NFAs. Fluorescence titration experiments indicated that MOF-1 exhibited remarkably low detection limits of 0.19 μM, 0.26 μM, and 0.34 μM for furazolidone (FZD), furaltadone (FDH) and nitrofurazone (NFZ), respectively. Meanwhile, MOF-1 was successfully employed for NFAs detection in real samples with the recoveries of 98.7 % - 104.1 %, and a relative standard deviation below 5.1 %. Moreover, the sensing mechanism could be ascribed to the synergistic effect between the internal filtering effect and photoinduced electron transfer according to the experiment results and DFT calculations. Additionally, test strips were prepared based on MOF-1 for point of care testing of NFAs.

Fabrication of Glucose Fluorescent Aptasensor Based on CdTe Quantum Dots

Diabetes is a chronic metabolic disease characterized by high blood glucose (or blood sugar) levels, which harms the heart, blood vessels, eyes, kidneys, and nerves over time. So, it is crucial to regularly control glucose concentration in biological fluids to check its targets, reduce unpleasant symptoms of high and low blood sugar, and avoid long-term diabetes complications. This study developed a simple, rapid, sensitive, and cost-effective fluorescence system for glucose determination. The fluorescent Aptasensor was fabricated using cadmium telluride quantum dots (CdTe QDs) modified with thioglycolic acid and functionalized with thiol-glucose-aptamer through ligand exchange. The thiol-glucose-aptamer interacted directly with CdTe QDs, increasing fluorescence intensity. However, it decreased when the target molecules of glucose were introduced. The structural and morphological characteristics of the Aptasensor were confirmed by various analytical methods such as UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). According to the typical Stern-Volmer equation, the relationship between fluorescent quenching and target concentration was linear with a detection limit (LOD) of 0.13 ± 1.95 × 10-11 mol L-1 and a relative standard deviation (RSD) of 1.05%. The Aptasensor demonstrated high specificity towards the target and stability over 28 days. Furthermore, it detected glucose in human serum and urine with a recovery rate of up to 99.74%. The results indicate that the fluorescent Aptasensor could be valuable in developing robust sensing technology for low-concentrated analytes.

A molecularly imprinted ratiometric fluorescent sensor for visual detection of 1-naphthol based on fluorescence-enhanced CdTeS QDs via APTES modification

CdTeS quantum dots (CdTeS QDs) were synthesized using the hydrothermal method and subsequently modified with (3-aminopropyl)triethoxysilane (APTES). This modification resulted in a significant enhancement of the fluorescence intensity, which was observed to be five times stronger than that of unmodified CdTeS QDs at 597 nm. Only after the fluorescence enhancement by APTES modification, the material showed a response to 1-naphthol (1-NP). Based on this, the molecularly imprinted polymers (MIPs) with ratiometric fluorescence were developed for the detection of 1-NP, that is, the synthetic raw material and the metabolite of the pesticide carbaryl. Under the excitation of 365 nm UV, the bright orange-red fluorescence (597 nm) of CdTeS QDs encapsulated in MIPs was quenched by 1-NP in the suspension, and 1-NP showed a gradually increasing blue emission (460 nm) with the increase of its concentration. This sensor has a good linear relationship between fluorescence intensity ratio (F460/F597) and 1-NP concentration (C1-NP) in a large concentration range (6.0-140.0 µM, LOD=0.45 µM, RSD<4.41%). It exhibits a visible fluorescence change from orange-red to blue-purple. Excellent recoveries in real samples were obtained by simulating carbaryl metabolism and demonstrated its potential in detection of 1-NP and carbaryl.

Silver nanopopcorns decorated on flexible membrane for SERS detection of nitrofurazone

The synthesis of three-dimensional silver nanopopcorns (Ag NPCs) onto a flexible polycarbonate membrane (PCM) for the detection of nitrofurazone (NFZ) on the fish surface by surface-enhanced Raman spectroscopy (SERS) is presented. The proposed flexible Ag-NPCs/PCM SERS substrate exhibits significant Raman signal intensity enhancement with the measured enhancement factor of 2.36 × 106. This is primarily attributed to the hotspots created on Ag NPCs, including numerous nanoscale protrusions and internal crevices distributed across the surface of Ag NPCs. The detection of NFZ by this flexible SERS substrate demonstrates a low limit of detection (LOD) of 3.7 × 10-9 M and uniform and reproducible Raman signal intensities with a relative standard deviation below 8.34%. It also exhibits excellent stability, retaining 70% of its efficacy even after 10 days of storage. Notably, the practical detection of NFZ in tap water, honey water, and fish surfaces achieves LOD values of 1.35 × 10-8 M, 5.76 × 10-7 M, and 3.61 × 10-8 M, respectively,  which highlights its effectiveness across different sample types. The developed Ag-NPCs/PCM SERS substrate presents promising potential for sensitive SERS detection of toxic substances in real-world samples.

A portable smartphone platform utilizing dual-sensing signals for visual determination of semicarbazide in food samples

Semicarbazide (SEM) is a metabolite of antibiotic nitrofurazone and a food contaminant in food production, showing potential carcinogenic, mutagenic, teratogenic, and toxic effects on human health. It is urgent to develop a highly efficient and sensitive assay for visual detection of SEM. In this paper, a pyrrolopyrrole cyanine fluorescent probe (PPCy-1) was reported for visualization and quantitative analysis of SEM through a chromophore reaction sensing mechanism for the first time. The probe towards SEM exhibited a fast response (10 min), a low detection limit (0.18 μM), high selectivity, and distinct dual ratiometric fluorescence turn-on and colorimetric modes. Its practicability was further verified by detecting SEM in meat, water, and honey samples with satisfactory recovery values. More importantly, a smartphone-assisted portable testing platform was constructed based on a PPCy-1-immobilized test paper or a polyamide thin film with a color scanning APP for real-time and on-site detection of SEM. This work provides low-cost, convenient, and rapid assays for visual SEM detection, which have potential applications in food safety monitoring.

Efficient sensitization of CdTe QDs towards PTCDA for sensitive photoelectrochemical Hg2+ assay

Herein, a sensitive photoelectrochemical (PEC) biosensor was designed for the detection of mercury ions (Hg2+) on the basis of the efficient sensitization of cadmium telluride quantum dots (CdTe QDs) towards 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and the significant quenching ability of a thymine-Hg2+-thymine (T-Hg2+-T) structure. The proposed CdTe QD/PTCDA sensitized structure was successfully constructed via continuous incubation of PTCDA and CdTe QDs on the glassy carbon electrode (GCE) interface, which embraced strong light absorption capacity and high carrier separation efficiency, giving rise to a remarkably improved initial photocurrent response. Notably, the PEC signal generated from the CdTe QD/PTCDA sensitized structure was almost fivefold higher than that of PTCDA owing to the efficient sensitization of CdTe QDs towards PTCDA. Once target Hg2+ ions were added, a T-rich S1 strand modified on the surface of 1-hexanethiol (HT)/S1/gold nanoparticles (Au NPs)/CdTe QDs/PTCDA/GCE immediately reacted with Hg2+ to produce multiple stable T-Hg2+-T structures. Therefore, the initial PEC signal would be considerably quenched by a high steric hindrance effect derived from the T-Hg2+-T structures. As a result, a quenched PEC response could achieve the detection of Hg2+ in concentrations ranging from 100 fM to 1000 nM. More importantly, the combination of the CdTe QDs/PTCDA sensitization structure and the T-Hg2+-T structure paves a promising pathway to developing a novel PEC biosensing platform for Hg2+ detection and also provides a favorable strategy for monitoring environmental pollution related to Hg2+.

Detection of enrofloxacin residues in dairy products based on their fluorescence quenching effect on AgInS2 QDs

Water-soluble AgInS₂ (AIS) quantum dots (QDs) were successfully prepared through the one-pot water phase method with thioglycolic acid (TGA) as the stabilizing agent. Because enrofloxacin (ENR) effectively quenches the fluorescence of AIS QDs, a highly-sensitive fluorescence detection method is proposed to detect ENR residues in milk. Under optimal detection conditions, there was a good linear relationship between the relative fluorescence quenching amount (ΔF/F₀) of AgInS₂ with ENR and ENR concentration (C). The detection range was 0.3125-20.00 μg/mL, r = 0.9964, and the detection limit (LOD) was 0.024 μg/mL (n = 11). The average recovery of ENR in milk ranged from 95.43 to 114.28%. The method established in this study has advantages including a high sensitivity, a low detection limit, simple operation and a low cost. The fluorescence quenching mechanism of AIS QDs with ENR was discussed and the dynamic quenching mechanism of light-induced electron transfer was proposed.