A simple assay platform for sensitive detection of Sudan I-IV in chilli powder based on CsPbBr3 quantum dots.

Sudan dyes are phenyl-azoic derivatives widely used in industry. Classified as carcinogenic and are strictly forbidden in foodstuffs; however, some unscrupulous businessmen adopted it for coloring foodstuffs. Here, a simple and effective fluorescence (FL) assay platform has been developed for the detection of Sudan I-IV based on CsPbBr3 perovskite quantum dots (QDs). It was found that the fluorescent emission of CsPbBr3 QDs can be effectively quenched by Sudan I-IV. Under the optimized conditions, the FL quenching efficiency of CsPbBr3 QDs was quantitatively correlated to the logarithmic concentrations of Sudan I-IV over the ranges of 100-10,000, 0.1-1000, 0.1-2000 and 0.4-1000 ng mL-1 for Sudan I-IV, and the corresponding limits of detection were 3.33, 0.03, 0.03 and 0.04 ng mL-1 (at 3σ/slope), respectively. CsPbX3 QDs (X = Cl, Br, and I or mixed halide systems Cl/Br and Br/I) was utilized as sensor in FL assay, which have unique optical properties of high FL quantum yields (up to 90%), narrow half peak width (26 nm) and tunable FL emissions spectra (410-700 nm). Meanwhile, the practical use of this assay platform for Sudan I-IV detection in chilli powder samples was also demonstrated, which indicated the potential in practical applications.

Silver triangular nanoplates as an high efficiently FRET donor-acceptor of upconversion nanoparticles for ultrasensitive "Turn on-off" protamine and trypsin sensor.

Silver triangular nanoplates (STNPs) as a high efficient fluorescence quenching reagent of upconversion nanoparticles (UCNPs) was used to constract a novel label-free fluorescence nanosensor for ultrasensitive detection of protamine and trypsin based on fluorescence resonance energy transfer (FRET) between STNPs and UCNPs. In this assay, the negatively charged STNPs can bind with positively charged UCNPs through electrostatic interaction, and then quenched the fluorescence of UCNPs. When protamine was added to the mixture of UCNPs-STNPs, the STNPs interacted with protamine and then detached from the surface of UCNPs and aggregated, which result in the recovery of the fluorescence of UCNPs. Trypsin could catalyze the hydrolysis of protamine and effectively quench the fluorescence recovered by protamine. By measuring the changes of the fluorescence of UCNPs, the concentrations of protamine and trypsin were determined. Under the optimized conditions, the linear response range was obtained from 10 to 500ng/mL, 5-80ng/mL and with the low detection limit of 3.1ng/mL and 1.8ng/mL for protamine and trypsin, respectively. Meanwhile, the nanosensor shows good selectivity, sensitivity and can be successfully applied to detection of protamine and trypsin in serum samples.

Glutathione regulation-based dual-functional upconversion sensing-platform for acetylcholinesterase activity and cadmium ions.

A dual-functional platform for the sensing of acetylcholinesterase (AChE) activity and cadmium ions (Cd2+) was developed based on the fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) via glutathione regulation. The detection mechanism is based on the fact that AuNPs can quench the fluorescence of UCNPs. AChE catalyzes the hydrolysis of acetylthiocholine (ATC) into thiocholine which reacts with AuNPs by S-Au conjunction and results the aggregation of AuNPs and change in fluorescence of UCNPs. Therefore, the AChE activity can be detected through the changes of the color of solution and fluorescence recovery of UCNPs. However, the presence of glutathione (GSH) can protect AuNPs from aggregation and enlarge the inter-particle distance between AuNPs and UCNPs. When Cd2+ is added into the stable mixture of AuNPs, GSH and AChE/ATC, Cd2+ could interact with GSH to form a spherical shaped (GSH)4Cd complex, which decreases the free GSH on the surface of AuNPs to weaken the stability of AuNPs and lead to the easily aggregation of them in the system. The aggregated-AuNPs are released from the surface of UCNPs, which results in the fluorescence of UCNPs gradually recovered. Under the optimized conditions, the detection limits of AChE activity and Cd2+ are estimated to be 0.015mU/mL and 0.2µM, respectively. The small molecules regulated dual-functional platform based on UCNPs/AuNPs is a simple, label-free method and can be applied for the turn-on fluorescence detection of AChE activity in human serum and Cd2+ in real water samples. The present work demonstrates a general strategy for the design of small molecules regulated multifunctional platform and will be expanded for different areas in the future.

Sensitive fluorescent detection of H2O2 and glucose in human serum based on inner filter effect of squaric acid-iron(III) on the fluorescence of upconversion nanoparticle.

Diabetes mellitus is an epidemic disease that it has became a worldwide public health problem. Thus, blood glucose monitoring has attracted extensive attention. Here, we report a nanosensor based on inner filter effect (IFE) between upconversion nanoparticles (UCNPs) and squaric acid (SQA)-iron(III) for the highly sensitive and selective detection of glucose levels in human serum. In this assay, GOx-catalyzed oxidization of glucose produces gluconic acid and hydrogen peroxide (H2O2). The latter can catalytically oxidize iron(II) to iron(III) which can rapidly (<1min) coordinate with the SQA to produce (SQA)-iron(III). The absorption band of (SQA)-iron(III) largely covered the emission band of UCNPs, resulting the fluorescence emission of UCNPs was effectively quenched. Therefore, the glucose can be monitored based on the formation of SQA-iron(III). Under the optimal condition, the fluorescence quenching efficiency shows a good linear response to glucose concentration in the ranges of 7-340µmol/L with a detection limit of 2.3µmol/L. The developed method has been further applied to monitor glucose levels in human serum with satisfactory results. Compared with other fluorescence methods, current method displayed high sensitivity and signal-to-noise ratio. Meanwhile, this nanosystem is also generalizable and can be easily expanded to the detection of various H2O2-involved analytes.

Universal Multifunctional Nanoplatform Based on Target-Induced in Situ Promoting Au Seeds Growth to Quench Fluorescence of Upconversion Nanoparticles.

Construction of a new multifunctional chemo/biosensing platform for small biomolecules and tumor markers is of great importance in analytical chemistry. Herein, a novel universal multifunctional nanoplatform for biomolecules and enzyme activity detection was proposed based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and target-inducing enlarged gold nanoparticles (AuNPs). The reductive molecule such as H2O2 can act as the reductant to reduce HAuCl4, which will make the Au seeds grow. The enlarged AuNPs can effectively quench the fluorescence of UCNPs owing to the good spectral overlap between the absorption band of the AuNPs and the emission band of the UCNPs. Utilizing the FRET between the UCNPs and enlarged AuNPs, good linear relationship between the fluorescence of UCNPs and the concentration of H2O2 can be found. Based on this strategy, H2O2 related molecules such as l-lactate, glucose, and uric acid can also be quantified. On the basis of UCNPs and PVP/HAuCl4, a general strategy for other reductants such as ascorbic acid (AA), dopamine (DA), or enzyme activity can be established. Therefore, the universal multifunctional nanoplatform based on UCNPs and the target-inducing in situ enlarged Au NPs will show its potential as a simple method for the detection of some life related reductive molecules, enzyme substrates, as well as enzyme activity.

Upconversion nanosensor for sensitive fluorescence detection of Sudan I-IV based on inner filter effect.

Sudan dyes are banned as food additives due to the carcinogenicity of their metabolites in the human body. Therefore, it is of great significance for sensitive detection of Sudan dyes. This paper reports a novel nanosensor for Sudan dyes detection based on fluorescence (FL) quenching of hexadecyl trimethyl ammonium bromide (CTAB) stabilized upconversion nanoparticles (UCNPs) through the inner filter effect (IFE). In the presence of Sudan I-IV, the fluorescence emission of UCNPs was effectively quenched due to the absorption bands of Sudan I-IV largely covered the emission bands of UCNPs. Under the optimized conditions, the FL was quenched with Sudan concentration over the range of 0.05-40, 0.01-20, 0.01-40 and 0.05-40 µg/mL for Sudan I-IV, respectively. The corresponding limit of detection is 15.1, 2.83, 3.52 and 16.7 ng/mL (at 3σ/slope) respectively. Meanwhile, the nanosensor shows good selectivity, sensitivity and can be successfully applied to detection of Sudan in chili powder samples.

Enzymatic-induced upconversion photoinduced electron transfer for sensing tyrosine in human serum.

This paper reports a novel nanosensor for tyrosine based on photoinduced electron-transfer (PET) between NaYF4:Yb, Tm upconversion nanoparticles (UCNPs) and melanin-like polymers. Melanin-like films were obtained from catalytic oxidation of tyrosine by tyrosinase, and deposited on the surface of UCNPs, and then quenched the fluorescence of UCNPs. Under the optimized conditions, the fluorescence quenching of UCNPs showed a good linear response to tyrosine concentration in the range of 0.8-100 µΜ with a detection limit of 1.1 µΜ. Meanwhile, it showed good sensitivity, stability and has been successfully applied to the detection of tyrosine in human serum.

Rapid and highly-sensitive uric acid sensing based on enzymatic catalysis-induced upconversion inner filter effect.

In this work, a novel and simple fluorescence method for detection of uric acid (UA) based on NaYF4:Yb(3+), Tm(3+) upconversion nanoparticles (UCNPs) is developed. The proposed method is based on the fact that uricase can oxidize uric acid to allantoin and hydrogen peroxide, which, on its turn, can oxidize o-phenylenediamine (OPD) to the oxidized OPD (oxOPD). The fluorescence of UCNPs can be significantly quenched by oxOPD through inner filter effects (IFE). Under the optimized conditions, the UA concentration was proportional to the changes in fluorescence intensity of UCNPs. A linear response was obtained over the concentration range from 20 to 850µΜ with the low detection limit of 6.7µΜ for uric acid. More importantly, this method has the potential to detect uric acid in human serum samples, suggesting the nanosensor can be used in a complex biological sample matrix.

Upconversion ratiometric fluorescence and colorimetric dual-readout assay for uric acid.

A new upconversion colorimetric and ratiometric fluorescence detection method for uric acid (UA) has been designed. Yb(3+), Er(3+) and Tm(3+) co-doped NaYF4 nanoparticles (UCNPs) was synthesized. The co-doped NaYF4 nanoparticles, emit upconversion fluorescence with four typical emission peaks centered at 490nm, 557nm, 670nm and 705nm under the 980nm near-infrared (NIR) irradiation. The ZnFe2O4 magnetic nanoparticles (MNPs) possessing excellent peroxidase-like activity was prepared and used to catalyze oxidation the coupling of N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt (TOPS) and 4-amino-antipyrine (4-AAP) in the presence of H2O2 to form purple products (compound 1) which has a characteristic absorption peak located at 550nm. The upconversion fluorescence at 557nm was quenched by the compound 1 while the upconversion emission at 705nm was essentially unchanged, the fluorescence ratio ((I557/I705)0/(I557/I705)) is positively proportional to UA concentration in existence of uricase. More importantly, colorimetric signal can be easily observed and applied to directly distinguish the concentration of UA by the naked eye. Under the optimized conditions, the linear range of colorimetric and ratiometric fluorescence sensing towards UA was 0.01-1mM, the detection limits were as low as 5.79µM and 2.86µM (S/N=3), respectively. The proposed method has been successfully applied to the analysis of UA in human serum. These results indicate that the colorimetric and ratiometric fluorescence dual-readout assay method has great potential for applications in physiological and pathological diagnosis.