Polymer surface ligand and silica coating induced highly stable perovskite nanocrystals with enhanced aqueous fluorescence for efficient Hg2+ and glutathione detection.

The poor stability and aqueous-quenching of fluorescence of perovskite nanocrystals (NCs) hinder their application in bio-detection and bio-imaging. Herein, through the synergistic effects of polymer surface ligand and silica encapsulation, highly stable and enhanced aqueous fluorescent CsPbBr3-mPEG@SiO2 NCs were synthesized and used as a novel "on-off-on" fluorescent probe for highly sensitive and selective detection of mercury ions (Hg2+) and glutathione (GSH) in aqueous solutions. The effects of the methoxypolyethylene glycol amine (mPEG-NH2) ligand and silica encapsulation on the stability and aqueous fluorescence of the CsPbBr3 NCs were studied. It indicated that the aqueous fluorescence of perovskite NCs was increased by 2.59 times. The water stability was also greatly improved, with the NCs maintaining 73% of their original fluorescence after storage for 30 days in water. X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) analyses further demonstrated that the NCs were successfully passivated by mPEG-NH2 and silica. The fluorescence of the CsPbBr3-mPEG@SiO2 nanocrystals was effectively quenched by Hg2+ which is attributed to the electron transfer process between NCs and Hg2+. Then, through the interaction between Hg2+ and GSH, the restoration of fluorescence for CsPbBr3-mPEG@SiO2 was realized. The "on-off-on" fluorescent probe can be used for the detection of Hg2+ and GSH with a low detection limit of 0.08 nM and 0.19 µM, respectively. It also shows a fast response time and high accuracy for practical sample detection. The simple and sensitive fluorescent probe of CsPbBr3-mPEG@SiO2 shows great potential in environmental and biological sensing.

A wearable sweat electrochemical aptasensor based on the Ni-Co MOF nanosheet-decorated CNTs/PU film for monitoring of stress biomarker.

Monitoring cortisol, a hormone released by the adrenal cortex in response to stress, is essential to evaluate the endocrine response to stress stimuli. While the current cortisol sensing methods require large laboratory settings, complex assay, and professional personnel. Herein, a novel flexible and wearable electrochemical aptasensor based on a Ni-Co metal-organic frameworks (MOF) nanosheet-decorated carbon nanotubes (CNTs)/polyurethane (PU) film is developed for rapid and reliable detection of cortisol in sweat. First, the CNTs/PU (CP) film was prepared by a modified wet spinning technology, and the CNTs/polyvinyl alcohol (PVA) solution was thermally deposited on the surface of CP film to form the highly flexible CNTs/PVA/CP (CCP) film with excellent conductivity. Then aminated Ni-Co MOF nanosheet prepared by a facile solvothermal method was conjugated with streptavidin and modified on the CCP film. Biofunctional MOF can effectively capture cortisol aptamer due to its excellent specific surface area. In addition, the MOF with peroxidase activity can catalytic oxidization of hydroquinone (HQ) by hydrogen peroxide (H2O2), which could amplify the peak current signal. The catalytic activity of Ni-Co MOF was substantially suppressed in the HQ/H2O2 system due to the formation of the aptamer-cortisol complex, which reduced the current signal, thereby realizing highly sensitive and selective detection of cortisol. The sensor has a linear range of 0.1-100 ng/mL and a detection limit of 0.032 ng/mL. Meanwhile, the sensor showed high accuracy for cortisol detection under mechanical deformation conditions. More importantly, the prepared MOF/CCP film based three-electrode was assembled with the polydimethylsiloxane (PDMS) substrate, and the sweat-cloth was used as the sweat collection channel to fabricate a wearable sensor patch for monitoring of cortisol in volunteers' sweat in the morning and evening. This flexible and non-invasive sweat cortisol aptasensor shows great potential for quantitative stress monitoring and management.

A highly-specific photoelectrochemical platform based on carbon nanodots and polymers functionalized organic-inorganic perovskite for cholesterol sensing.

Herein, we reported the introduction of carbon nanodots (CNDs) and polyvinylidene fluoride (PVDF) as additives into perovskite CH3NH3PbI3 through in situ synthesis to prepare PVDF-CH3NH3PbI3@CNDs composite, which demonstrated improved water tolerance and mechanical stability. The application of PVDF-CH3NH3PbI3@CNDs for photoelectrochemical sensing was then explored. A molecularly imprinted polymer (MIP) that could specifically recognize cholesterol (CHO) was anchored to PVDF-CH3NH3PbI3@CNDs via a simple thermal polymerization process, followed by elution with hexane. A label-free and sensitive photoelectrochemical method for CHO detection was achieved by using the MIPs@PVDF-CH3NH3PbI3@CNDs platform. The detection limit for CHO was 2.1 × 10-14 mol/L, lower than most of the existing CHO detection methods. In our perception, this platform can be extended to numerous other analytes. This research result may provide a new understanding to improve the performance and broaden the application range of organic-inorganic perovskites.