Smartphone colorimetric determination of hydrogen peroxide in real samples based on B, N, and S co-doped carbon dots probe.

In this paper, we report the use of a smartphone and B, N, and S co-doped carbon dots (BNS-CDs) as a promising peroxidase mimic to quantify hydrogen peroxide (H2O2). The synthesized BNS-CDs exhibited excellent peroxidase-like activity to catalyze the reaction of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) with H2O2 to generate a blue oxide product (ox-TMB) with maximum absorption at 652 nm. Steady-state kinetic analysis demonstrated that the BNS-CDs showed much higher affinity than natural horseradish peroxidase (HRP) for H2O2 due to their small size and larger specific surface area. A smartphone colorimetric readout device was employed to record the RGB (red green blue) value of the ox-TMB solution via the Android application Color Grab for quantitative detection. A good linear relationship (R2 = 0.9970) between the H2O2 concentration and |R-Rblank| value was obtained in the range of 3-30 µM with a limit of detection (LOD) of 0.8 µM. The current method was successfully applied to determine H2O2 in mouthwash and milk with recoveries of 92.70-108.30%. The developed assay is a promising portable detection platform for H2O2 with good sensitivity and selectivity, simple operation, fast response, and low cost. Graphical abstract.

Dual-emission ratio fluorescent probes based on carbon dots and gold nanoclusters for visual and fluorescent detection of copper ions.

Blue carbon dots (BCDs) and red gold nanoclusters modified by bovine serum albumin (BSA-Au NCs) were selected as luminescent nanomaterials, and the nanohybrid materials were successfully prepared and applied to the fluorescent measurement of copper ions. The prepared ratio fluorescent probe has two emission peaks near 452 and 654 nm under an excitation of 330 nm. The fluorescence intensity was gradually quenched because Au NCs was aggregated in the presence of Cu2+, resulting in a gradation of the fluorescent color from red to pink to purple to blue for visual detection. BCDs have almost the same fluorescence intensity due to their light stability and chemical inertness to Cu2+ and serve as a background reference in the sensing system. Under the optimal condition, the detection limit (LOD) is 16 nM, the linear range is 0.05-1.85 µM, and the coefficient of determination R2 is 0.9987 for copper determination. Compared with other single probes, the ratio fluorescent probe in the current study has good water solubility, low cytotoxicity, and is easy to synthesize. The nanoprobe provides a high-quality and sensitive visible light platform for monitoring copper ions. Graphical abstract.

Quantitative Visual Detection of Mercury Ions With Ratiometric Fluorescent Test Paper Sensor.

A novel ratiometric fluorescence probe based on nitrogen-doped blue carbon dots (NCDs) and red gold nanoclusters (Au NCs) for mercuric ion (Hg2+) has been prepared and characterized. A user friendly fluorescent test paper based sensor combined with smartphone was fabricated for rapid visual and quantitative detection. Hg2+ can specifically bind to Au+ on the surface of Au NCs, leading to the quench of red fluorescence while the fluorescence intensity of the NCDs with blue fluorescence remained unchanged as a internal standard signal. The implement of paper-based sensor address some common drawback in analytical process such as the detection time, analysis cost. In a further demonstration, a homemade detection device with smartphone was used to qualify the Hg2+. After adding different concentration of Hg2+, red, purple, and blue colors were obtained on the detection zones of the fluorescent test paper. The Android App Color Grab was used to identify the red, green and blue (RGB) values of fluorescent color. The rapid visual and quantitative detection of Hg2+ was accomplished with the detection limit of 2.7 nM for fluorescence, 25 nM for smartphone and 32 nM for paper strip. The developed multi-mode detection platform was successfully applied to the detection of mercury ions in water samples with acceptable recoveries. The NCDs and Au NCs probe facilitate the one-site environmental monitoring for Hg2+ with "naked-eye" and smartphone.