Covalent Surface Functionalization of Semiconducting Polymer Dots with β‑Cyclodextrin for Fluorescent Ratiometric Assay of Cholesterol through Host–Guest Inclusion and FRET

Special functionalization of semiconducting polymer dots (Pdots) is highly desired to expand their applications in chemo/biosening. Herein, carboxyl-functionalized poly­[(9,9-dioctylfluorenyl-2,7-diyl)-<i>co</i>-(1,4-benzo-{2,1′,3}-thiadiazole)] dots covalently tagged with aminated β-cyclodextrin (NH₂–CD) have been designed to construct a ratiometric sensor for cholesterol (Cho). Using CD-Pdots as energy donors with rhodamine B (RB) as energy acceptors, a fluorescence resonance energy transfer (FRET) pair has been built because the host–guest interaction between RB and CD attached to Pdots brings donors and acceptors into close proximity. In the presence of Cho, the acceptors will depart from the donors because of the competitive inclusion interaction between Cho and RB with CD, resulting in the hindering of the FRET process between CD-Pdots and RB. On the basis of the turn-on fluorescence of CD-Pdots and turn-off fluorescence of RB, a sensitive ratiometric method for the determination of Cho in the concentration range from 25 to 350 nM with a detection limit of 4.9 nM was achieved. The proposed method was validated to determine free Cho in human serum samples with satisfactory results

A Mitochondria-Targeted Ratiometric Biosensor for pH Monitoring and Imaging in Living Cells with Congo-Red-Functionalized Dual-Emission Semiconducting Polymer Dots

The accurate and sensitive monitoring and imaging of mitochondrial pH in living cells play vital roles in chemical biology and biomedicine. Herein, we design a novel ratiometric fluorescent chemical probe for monitoring and imaging the pH of mitochondria in living cells based on congo-red (CR)-modified dual-emission semiconducting polymer dots (Pdots) via a competitive fluorescence resonance energy transfer (FRET) mechanism. The Pdots are synthesized by triphenylphosphonium (TPP)-modified polyoxyethylene nonylphenylether (CO-520), poly­(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly­(9,9-dioctylfluorene)-<i>co</i>-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PF-DBT5), and poly­(styrene-<i>co</i>-maleic anhydride) (PSMA) via a nanoprecipitation method, and the prepared Pdots are further chemically linked with pH-sensitive, nonfluorescent CR to obtain the mitochondria-targeted pH fluorescent probes. This Pdots-based probe consists of two luminescent components including PFO and PF-DBT5 as fluorescence donors, an acid–base indicator CR as an energy acceptor, and TPP as the mitochondria-targeting group. At a different pH region, the FRET efficiency between CR and PFO or CR and PF-DBT5 can be modulated. This probe exhibits good biocompatibility, a wide pH detection range from 2.57 to 8.96, good reversibility, high selectivity, and excellent photostability for pH monitoring. This probe allows for the detecting and imaging of mitochondrial pH in living cells with satisfactory results

Mediatorless Glucose Biosensor and Direct Electron Transfer Type Glucose/Air Biofuel Cell Enabled with Carbon Nanodots

Utilization of carbon nanodots (CNDs), newcomers to the world of carbonaceous nanomaterials, in the electrochemistry realm has rarely been reported so far. In this study, CNDs were used as immobilization supports and electron carriers to promote direct electron transfer (DET) reactions of glucose oxidase (GOx) and bilirubin oxidase (BOD). At the CNDs electrode entrapped with GOx, a high rate constant (<i>k</i>_s) of 6.28 ± 0.05 s^–1 for fast DET and an apparent Michaelis–Menten constant (<i>K</i>_M^app) as low as 0.85 ± 0.03 mM for affinity to glucose were found. By taking advantage of its excellent direct bioelectrocatalytic performances to glucose oxidation, a DET-based biosensor for glucose detection ranging from 0 to 0.64 mM with a high sensitivity of 6.1 μA mM^–1 and a limit of detection (LOD) of 1.07 ± 0.03 μM (S/N = 3) was proposed. Additionally, the promoted DET of BOD immobilized on CNDs was also observed and effectively catalyzed the reduction of oxygen to water at the onset potential of +0.51 V (vs Ag/AgCl). On the basis of the facilitated DET of these two enzymes at CNDs electrodes, a mediator-free DET-type glucose/air enzymatic biofuel cell (BFC), in which CNDs electrodes entrapped with GOx and BOD were employed for oxidizing glucose at the bioanode and reducing oxygen at the biocathode, respectively, was successfully fabricated. The constructed BFC displayed an open-circuit voltage (OCV) as high as 0.93 V and a maximum power density of 40.8 μW cm^–2 at 0.41 V. These important features of CNDs have implied to be promising materials for immobilizing enzymes and efficient platforms for elaborating bioelectrochemical devices such as biosensors and BFCs

Colorimetric and Phosphorimetric Dual-Signaling Strategy Mediated by Inner Filter Effect for Highly Sensitive Assay of Organophosphorus Pesticides

We describe here a colorimetric and phosphorimetric dual-signaling strategy for sensitive assay of organophosphorus pesticides (OPPs). The principle for assay depends on the phenomenon that the phosphorescence of Mn-ZnS quantum dots (QDs) can be dramatically quenched by Au nanoparticles (AuNPs) through the inner filter effect (IFE) and the activity of acetylcholinesterase (AChE), an enzyme that catalytically hydrolyzes acetylthiocholine to thiocholine that can be inhibited by OPPs. By virtue of the variations of absorbance and phosphorescence of the analytical system, a dual-readout assay for OPPs has been proposed. The limits of detection for different OPPs including paraoxon, parathion, omethoate, and dimethyl dichlorovinyl phosphate (DDVP) are found to be 0.29, 0.59, 0.67, and 0.44 ng/L, respectively. The proposed assay was allowed to detect pesticides in real spiked samples and authentic contaminated apples with satisfactory results, suggesting its potential applications to detect pesticides in complicated samples