The Development of the Fluorescence-based Portable Device for Lead (II) and Formalin Determination in Food Samples by Using Nitrogen-Doped Carbon Dots (N-CDs).

The fluorescence-based portable device for the determination of lead (Pb2+) and formalin (FA) in food samples by using Nitrogen-doped carbon dots (N-CDs) as a fluorescence probe was developed. The proposed approach, Pb2+, and FA were determined based on the photo-induced electron transfer (PET) mechanism and the silver mirror reaction. The fluorescence intensity of the N-CDs decreased with the increase of Pb2+ concentration and increased with the increasing FA concentration. The fluorescence intensity of N-CDs after the reactions were measured by a filter-free fluorometer platform using a commercial camera module and a Raspberry Pi, a compact computer, as a detector and processor. The experimental results were obtained using control samples with known Pb2+ and FA concentrations in the 0.01-10 mg L- 1 and 25-150 mg L- 1, respectively. The proposed approach is simple, low-cost, and accurate for the on-site monitoring of Pb2+ and FA in various food samples. Of utmost importance, the proposed approach is expected to be a pioneering model for the future development of other analytes with a broad range of practical applications.

Portable device for dual detection of fluorescence and absorbance for biosensing or chemical sensing applications.

Early detection is key to prevent health problems and could be performed by biosensors and chemical sensors. However, a lot of them still need bulky benchtop equipment. This work presents a portable device for measuring fluorescence and light absorption that can be used with optical biosensors or chemical sensors. It uses a small laser diode as a light source and three filter-mounted photodiodes as detectors, all of which are inexpensive, customizable and widely available commercially. The results from our device show good correlation with that from commercial instruments. Therefore, it could be beneficial for early or on-site detection.

Fluorescent cysteine probe based on a signal amplification unit, a catalyzed hairpin assembly reaction and Förster resonance energy transfer.

This work developed a sensitive DNA-based fluorescent probe comprising a cysteine binding unit and a signal amplification unit based on a catalyzed hairpin assembly (CHA) reaction. The cysteine binding unit comprises a homodimer of single-stranded DNA (ssDNA) rich in cytosine and held together by silver ions. In the presence of cysteine, the homodimer is disintegrated because of cysteine-silver binding that liberates the ssDNA, which drives the CHA reaction in the signal amplification unit. Förster resonance energy transfer (FRET) was used to report the generation of the amplified double-stranded DNA (dsDNA) product. Under the optimal conditions, the probe provided a good linearity (100-1200 nM), a good detection limit (47.8 ± 2.7 nM) and quantification limit (159.3 ± 5.3 nM), and a good sensitivity (1.900 ± 0.045µM-1). The probe was then used to detect cysteine in nine real food supplement samples. All results provided good recoveries that are acceptable by the AOAC, indicating that it has potential for practical applications.