Near-infrared Ag2S Quantum Dots Research Articles

Dual-mode fluorescence and colorimetric sensing of sulfide anion in natural water based on near-infrared Ag2S quantum dots and MnO2 nanosheets complex

Near infrared (NIR) emission Ag2S quantum dots (QDs) are of great value for biochemical sensing with strong anti-interference and low toxicity. Herein, NIR fluorescence Ag2S QDs were synthesized successfully. Combined with the excellent oxidase-like characteristics of manganese dioxide (MnO2) nanosheets, a fluorescence and colorimetric dual-mode sensor for sulfide anion was developed. MnO2 nanosheets could effectively catalyze the oxidation of TMB to produce blue TMB oxide (ox TMB), at the same time, the fluorescence of Ag2S QDs could be effectively quenched by fluorescence internal filtration effect (IFE) and dynamic quenching effect. The enzyme-like activity was weakened and the NIR fluorescence of Ag2S QDs was restored when sulfide anion (S2−) was added, due to the reduction of MnO2 to Mn2+.The linear ranges for fluorescence and colorimetric analysis of S2− were 2–250 μM and 0.3–50 μM, with detection limits of 0.6 and 0.215 μM, correspondingly. The dual-mode sensor had a wider detection range, higher sensitivity and shorter reaction time, which could be used for highly selective detection of S2− in different concentration ranges. In addition, it had been successfully applied to the determination of sulfide in water samples with satisfactory accuracy and sensitivity.

A ratiometric fluorescent assay for the detection and bioimaging of alkaline phosphatase based on near infrared Ag2S quantum dots and calcein

Herein, a ratiometric fluorescent method was developed for alkaline phosphatase (ALP) detection based on near-infrared (NIR) Ag2S quantum dots (QDs) and calcein through the competitive approach. The system based on Ag2S QDs and calcein shows green (maximum emission at 512 nm from calcein) and near infrared (NIR) fluorescence (maximum 798 nm from Ag2S QDs) under the same excitation wavelength (468 nm). In the presence of Ce3+, the fluorescence intensity of calcein is decreased due to static quenching, while the fluorescence intensity of Ag2S QDs is enhanced through aggregation induced emission (AIE). The p-nitrophenyl phosphate is hydrolyzed by ALP, and the yield phosphate ions bind with Ce3+ with higher affinity than these of Ag2S QDs and calcein. Therefore, the green fluorescence from calcein is recovered while NIR fluorescence from Ag2S QDs is decreased. On the basis of these findings, a ratiometric fluorescence assay was developed for the measurement of ALP activity. The ratio of fluorescence intensity at 512 and 798 nm (F512/F798) was well associated with the ALP concentration ranging from 2 to 100 mU/mL with the detection limit of 1.28 mU/mL. The method was successfully applied for detecting ALP in human serum with an acceptable recovery and bioimaging intracellular ALP with good performance. In addition, the approach was also employed for the screening ALP inhibitor.

Label-free fluorometric assay for cytochrome c in apoptotic cells based on near infrared Ag2S quantum dots

As an important biomarker, cytochrome c (Cyt c) plays a crucial role in mitochondrial electron transport chain and cell apoptosis. Herein, a label-free near-infrared (NIR) Ag2S quantum dots (QDs)-based fluorescent strategy was constructed for the sensitive and selective detection of Cyt c. In this system, Cyt c was hydrolyzed by trypsin, and the resulting heme-peptide fragment exhibited peroxidase-like activity for catalytic decomposition of H2O2 into hydroxyl radical (·OH). The presence of caffeic acid in this system resulted into the formation of caffeic acid-quinone due to the strong oxidizing ability of ·OH. The production of caffeic acid-quinone led to the fluorescence quenching of Ag2S QDs through electron transfer mechanism. Based on the cascade reaction, we successfully developed a label-free approach to detect Cyt c using Ag2S QDs as nanoprobes. Under the optimized conditions, the fluorescence intensity of Ag2S QDs was linearly relative to the concentration of Cyt c over the range from 2.0 to 150 nM with a detection limit of 1.7 nM. In addition, this strategy was successfully applied for quantitative detection of Cyt c in cell lysates of H2O2 or etoposide (anticancer drug)-induced apoptotic cells, providing great potential application for cell-based oxidation pressure determination and screening of anticancer drugs.

A Novel Fluorescent Nanoparticle for Sensitive Detection of Cry1Ab Protein In Vitro and In Vivo

Here, we report the synthesis and characterization of CoFe2O4 doping Ag2S dendrimer-modified nanoparticles (CoFe2O4-Ag2S DMNs) in Cry1Ab protein detection and imaging. The near-infrared Ag2S quantum dots were first prepared by using the thermal decomposition method, followed by modification of the water-soluble quantum dots using the method of solvent evaporation and ligand exchange, and finally the fluorescent magnetic bifunctional nanoparticles were obtained by binding with CoFe2O4. As-prepared CoFe2O4-Ag2S DMNs were characterized by fluorescence (FL) spectroscopy and transmission electron microscopy (TEM). Results showed that Ag2S DMNs could sensitively detect Cry1Ab both in vitro and in vivo. In vitro, the enhanced FL intensity as a function of the concentration is notably consistent with the Langmuir binding isotherm equation in the range of 0-200ng/mL of Cry1Ab proteins. The detection limit of this method was found to be 0.2ng/mL. Meanwhile, the fluorescence wavelength was extended to the second near-infrared range (NIR-II, 1.0~1.4μm), which enables in vivo imaging. This study highlights the importance of NIR QDs doping magnetic materials as a new method to trace Bacillus thuringiensis (Bt) in insects and their potential applications in in vivo NIR tissue imaging.