Jiajia Guo

Sensitive fluorescent detection of melamine in raw milk based on the inner filter effect of Au nanoparticles on the fluorescence of CdTe quantum dots

A simple, rapid and sensitive fluorescent assay for determination of melamine has been developed based on inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). When thioglycolic acid-capped CdTe QDs was mixed with citrate-stabilized AuNPs, the fluorescence of CdTe QDs was significantly quenched via the IFE of AuNPs. With the presence of melamine, melamine could induce the aggregation and corresponding absorbance change of AuNPs, which then resulted in the recovery of IFE-decreased emission of CdTe QDs. Under the optimum conditions, the detection limit for melamine in raw milk was 0.02mgL(-1). The application of this method in samples of melamine-spiked raw milk suggested a recovery between 103% and 104%. Therefore, the obvious merits provided by the present assay, such as simplicity, rapidity, low cost, and high sensitivity, would make it promising for on-site screening of melamine adulterant in raw milk.

Visual detection of organophosphorus pesticides represented by mathamidophos using Au nanoparticles as colorimetric probe.

With citrate-coated Au nanoparticles as colorimetric probe, a novel visual method for rapid assay of organophosphorus pesticides has been developed. The assay principle is based on catalytic hydrolysis of acetylthiocholine into thiocholine by acetylcholinesterase, which induces the aggregation of Au nanoparticles and the color change from claret-red to purple or even grey. The original plasmon absorption of Au nanoparticles at 522 nm decreases, and simultaneously, a new absorption band appears at 675 nm. The irreversible inhibition of organophosphorus pesticides on acetylcholinesterase prevents aggregation of Au nanoparticles. Under optimum conditions, the absorbance at 522 nm of Au nanoparticles is related linearly to the concentration of mathamidophos in the range of 0.02-1.42 μg/mL with a detection limit of 1.40 ng/mL. This colorimetric method has been successfully utilized to detect mathamidophos in vegetables with satisfactory results. The proposed colorimetric assay exhibits good reproducibility and accuracy, providing a simple and rapid method for the analysis of organophosphorus pesticides.

Efficient fluorescence resonance energy transfer between oppositely charged CdTe quantum dots and gold nanoparticles for turn-on fluorescence detection of glyphosate.

We designed a turn-on fluorescence assay for glyphosate based on the fluorescence resonance energy transfer (FRET) between negatively charged CdTe quantum dots capped with thioglycolic acid (TGA-CdTe-QDs) and positively charged gold nanoparticles stabilized with cysteamine (CS-AuNPs). Oppositely charged TGA-CdTe-QDs and CS-AuNPs can form FRET donor-acceptor assemblies due to electrostatic interactions, which effectively quench the fluorescence intensity of TGA-CdTe-QDs. The presence of glyphosate could induce the aggregation of CS-AuNPs through electrostatic interactions, resulting in the fluorescence recovery of the quenched QDs. This FRET-based method has been successfully utilized to detect glyphosate in apples with satisfactory results. The detection limit for glyphosate was 9.8 ng/kg (3σ), with the linear range of 0.02-2.0 μg/kg. The attractive sensitivity was obtained due to the efficient FRET and the superior fluorescence properties of QDs. The proposed method is a promising approach for rapid screening of glyphosate in real samples.

Aptamer-based fluorescent screening assay for acetamiprid via inner filter effect of gold nanoparticles on the fluorescence of CdTe quantum dots.

AbstractThis paper reports a novel aptamer-based fluorescent detection method for small molecules represented by acetamiprid based on the specific binding of aptamers with acetamiprid, and the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (CdTe QDs). When CdTe QDs were mixed with AuNPs, the fluorescence of CdTe QDs was significantly quenched via IFE. The IFE efficiency could be readily modulated by the absorption and the aggregation state of AuNPs. The presence of salt could easily induce the aggregation of AuNPs, resulting in the fluorescence recovery of the quenched QDs. Acetamiprid-binding aptamer (ABA) could adsorb on the negatively charged AuNPs through the coordination interaction to protect AuNPs from salt-induced aggregation, so the fluorescence of CdTe QDs would be quenched by the IFE of AuNPs. However, the specific binding of ABA with acetamiprid could release the ABA from the surfaces of AuNPs and decrease the salt tolerance of AuNPs, so the IFE-decreased fluorescence of CdTe QDs was regained with the presence of acetamiprid, and the fluorescence enhancement efficiency was driven by the concentration of acetamiprid. Based on this principle, the aptamer-based fluorescent method for acetamiprid has been established and optimized. The assay exhibited excellent selectivity towards acetamiprid over its analogues and other pesticides which may coexist with acetamiprid. Under the optimum experiment conditions, the established method could be applied for the determination of acetamiprid with a wide linear range from 0.05 to 1.0 μM, and a low detection limit of 7.29 nM (3σ). Furthermore, this IFE-based method has been successfully utilized to detect acetamiprid in six types of vegetables, and the results were in full agreement with those from HPLC and LC-MS. The proposed method displays remarkable advantages of high sensitivity, rapid analysis, excellent selectivity, and would be suitable for the practical application of target screening in real samples. Graphical Abstractᅟ

Facile synthesis of chitosan-capped ZnS quantum dots as an eco-friendly fluorescence sensor for rapid determination of bisphenol A in water and plastic samples

This paper describes a novel eco-friendly fluorescence sensor for determination of bisphenol A (BPA) based on chitosan-capped ZnS quantum dots (QDs). By using safe and inexpensive materials, nontoxic ZnS QDs were synthesized via an environment-friendly method using chitosan as a capping agent. The as-prepared ZnS QDs exhibited characteristic absorption (absorbance edge at 310 nm) and emission (maxima at 430 nm) spectra with a relatively high fluorescence quantum yield of 11.8%. Quantitative detection of BPA was developed based on fluorescence quenching of chitosan-capped ZnS QDs with high sensitivity and selectivity. Under optimal conditions, the fluorescence response of ZnS QDs was linearly proportional to BPA concentration over a wide range from 0.50 to 300 μg L−1 with a detection limit of 0.08 μg L−1. Most of the potentially coexisting substances did not interfere with the BPA-induced quenching effect. The proposed analytical method for BPA was successfully applied to water and plastic real samples. The possible quenching mechanism is also discussed.

Highly sensitive turn-on fluorescent detection of cartap via a nonconjugated gold nanoparticle–quantum dot pair mediated by inner filter effect

Here, we describe a simple fluorometric assay for the highly sensitive detection of cartap on the basis of the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdTe quantum dots (QDs). In the presence of AuNPs, the fluorescence of CdTe QDs was significantly quenched due to the intensive absorption of AuNPs at the 522 nm plasmon band. The well-dispersed AuNPs exhibited a tendency to aggregate when exposed to cartap with positively charged amine groups, which induced an absorption band transition from 522 nm to the long-wavelength band and restored the IFE-decreased emission of CdTe QDs for cartap detection. Under optimum conditions, the response was linearly proportional to the concentration of cartap in Chinese cabbage within the range of 0.01 to 0.50 mg kg−1 with a detection limit of 8.24 μg kg−1 (S/N = 3). Further application in cartap-spiked vegetable samples suggested a recovery between 81.9% and 90.6%. The amount of cartap in the spiked samples detected by the present method and GC-MS was in good accordance, which indicates that this IFE-based fluorescent method is reliable and practical. The proposed assay exhibited good reproducibility and accuracy, providing a simple and rapid method for the analysis of cartap.