A smartphone-assisted fluorescent sensing platform for ochratoxin A using Mn-doped CsPbBr3 perovskite quantum dots embedded in the mesoporous silica as a ratiometric probe.

Food sources are susceptible to contamination with ochratoxin A (OTA), which is a serious threat to human health. Thus, the construction of novel, simple sensing platforms for OTA monitoring is of utmost need. Manganese-doped lead halide perovskite quantum dots encapsulated with mesoporous SiO2 (Mn-CsPbBr3 QDs@SiO2) were prepared here and used as a ratiometric fluorescent probe for OTA. Mn-CsPbBr3 QDs, synthesized at room temperature, exhibit dual emission with maximum wavelengths of 440 and 570 nm and, when embedded in the SiO2 layer, produce a stable and robust photoluminescence signal. By adding OTA to the probe, emission at 440 nm increases while emission at 570 nm decreases, so a ratiometric response is obtained. Experimental variables affecting the probe signal were studied and optimized and the mechanism of sensing was discussed. This ratiometric sensor demonstrated excellent selectivity and low detection limit (4.1 ng/ml) as well as a wide linear range from 5.0 to 250 ng/ml for OTA. A simple portable smartphone-based device was also constructed and applied for the fluorescence assay. With different OTA concentrations, the multicolor transition from pink to blue under a UV lamp led to simple visual and smartphone-assisted sensing of OTA by using a color analyzing application. Satisfactory recoveries in black tea, coffee, moldy fig and flour samples confirmed the reliability of the assay. The accuracy of the probe was proved by comparison of the results with high-performance liquid chromatography (HPLC).

Perovskite quantum dots as a chemiluminescence platform for highly sensitive assay of cefazolin.

This paper reports on a chemiluminescence (CL) probe consist of CsPbBr3 quantum dots (QDs) in organic phase together with Fe(II) and K2S2O8 in aqueous medium for the highly selective and sensitive determination of the antibiotic, cefazolin (CFZ). The CsPbBr3perovskite QDs prepared by the ligand assisted reprecipitation method, exhibit a narrow fluorescence at 533 nm under 460 nm excitation with a high quantum yield (42 %). The Fe(II) - S2O82- as an ultra-weak CL system is converted to a rather strong CL sensing platform in the presence of organic-phase CsPbBr3 QDs. It was observed that CFZ exerts an enhancement effect on the CL signal of the designed probe in the linear range of 25 - 300 nM, with a low limit of detection (9.6 nM). The introduced sensor has broad application prospects in biosensing, food detection, and other fields with recovery ranging from 94 to 106 %.

A dual colorimetric and fluorometric sensor based on N, P-CDs and shape transformation of AgNPrs for the determination of 6-mercaptopurine.

In this study, we designed a dual colorimetric and fluorometric sensor by using nitrogen and phosphor doped carbon dots (N, P-CDs) and Ag nanoprisms (AgNPrs) to detect 6-mercaptopurine (6-MP). For this purpose, we applied the AgNPrs/I- mixture to establish a shape transformation based colorimetric method for the detection of 6-MP. The assay mechanism of colorimetric method was based on etching and protecting effect of I- and 6-MP on the AgNPrs. In the presence of I-, as an etching agent, the solution color altered from blue to purple and the position of AgNPrs' local surface plasmon resonance (LSPR) peak shifted to the blue wavelengths. This phenomenon was assigned to the morphological change of AgNPrs. In the presence of 6-MP, AgNPrs were protected from etching by I-, so the LSPR peak position and solution color of AgNPrs remained unchangeable. Furthermore, the fluorescence intensity of N, P-CDs decreased with adding AgNPrs/I- due to the spectral overlap between etched AgNPrs and N, P-CDs. The CDs' quenched fluorescence was restored in the presence of 6-MP, as a result of the protecting effect of 6-MP on the AgNPrs. These facts have been applied to develop a dual sensor for the determination of 6-MP at the range of 10-500 nM and 30-500 nM by colorimetric and fluorometric detection methods. The detection limits were obtained 10 and 4 nM for fluorometric and colorimetric methods, respectively. The developed sensor was utilized for dual signal analysis of 6-MP in human serum samples with satisfactory results.

A sensitive colorimetric probe for detection of 6-thioguanine based on its protective effect on the silver nanoprisms.

In this work a non-aggregated colorimetric probe for detection of chemotherapeutic drug, 6-thioguanine (6-TG), is introduced. It is based on the protective effect of 6-TG on silver nanoprisms (AgNPRs) against the iodide-induced etching reaction. Iodide ions can attack the corners of AgNPRs and etch them, leading to the morphological transition from nanoprisms to nanodiscs. As a consequence, the solution color changes from blue to pink. However, in the presence of 6-TG, due to its protective effect on the corners of AgNPRs, I- ions cannot etch the prisms and the blue color of solution remains unchanged. Using this effect, selective sensor was designed for detection of 6-TG in the range of 2.5-500 µg L-1, with a detection limit of 0.95 µg L-1. Since with varying the concentration of 6-TG in this range, the color variation from pink to blue can be easily observed, the designed sensing scheme can be used as a colorimetric probe. The method was used for analysis of human plasma samples.