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l -cysteine (L-Cys) plays an important role in human health as well as in the biological environment. Here, a simple physical mixing technique was used to create the p-n heterojunction by homogeneously immobilizing cuprous oxide/copper@microporous carbon (Cu 2 O/Cu@mC) on the surface of a sheet of g-C 3 N 4 (CNS). Among them, the porous structure of Cu 2 O/Cu@mC after heat treatment is favorable for charge storage. Meanwhile, the carbon element in Cu 2 O/Cu@mC acts as a photosensitizer and electron mediator to extend visible light absorption. Compared with bulk g-C 3 N 4 (CNB), the sheet-like structure and high specific surface area of CNS can be used as a carrier for the binding of Cu 2 O/Cu@mC with L-Cys. Based on the interaction between L-Cys and Cu 2 O/Cu@mC through the formation of Cu–S bonds, Cu 2 O/Cu@mC/CNS was proposed as a light-driven enzyme-free photoelectrochemical sensor for the detection of L-Cys. In the best case, the Cu 2 O/Cu@mC/GCE sensor has a low limit of detection of 1.26 × 10−9 M for L-Cys and a wide linear range (1.0 × 10−8 M − 4.0 × 10−6 M). The repeatability, reproducibility, stability, selectivity and specificity of the sensor were satisfactory. In addition, the potential applicability of the proposed photoelectrochemical sensor was evaluated in tap water and human serum. [Display omitted] • A low-cost and simple method to detect L-Cys in tap water and human serum. • The Cu 2 O/Cu@mC/CNS has excellent chemical stability and high selectivity. • It is a highly sensitive enzyme-free PEC sensor composed of p-n heterostructure. • The constructed PEC sensor has an ultra-low LOD and an ultra-wide linear range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cauliflower-like CdS with the rough and wide surface was created. • The CdS/rGO@Au/GCE sensor has wide linear range (5 nM − 4 μM). • The detection limit of 2.88 nM is 10,000-fold lower than the WHO guideline. • The sensor has been used to analyze Cu(II) in pool water with great performance. • Material-target interaction is used to solve the selectivity problem of PEC sensors. Copper (II) ion (Cu2+) is a typical heavy metal ion that not only harms the soil and water environment, but also causes neurological disorders, liver cirrhosis and other diseases. Here, we have successfully synthesized three-dimensional CdS/rGO@Au heterojunction using a simple physical mixing technique, characterized the material synthesis by X-ray diffraction spectroscopy (XRD), Transmission electron microscopy (TEM), and finally used it for selective photoelectrochemical detection of Cu2+. In this system, the synergistic interaction of the three creates a channel that is ideal for charge carrier separation and transfer. The cauliflower-shaped CdS possesses a large surface area and acts as a Cu2+ probe. rGO@Au acts as a sensitizer and amplifies the current change. The photocurrent of the CdS/rGO@Au heterojunction is 7 times higher than that of CdS, indicating that CdS/rGO@Au has a good photoresponse intensity. Under the optimized detection conditions, the proposed photoelectrochemical sensor was able to detect Cu2+ concentration in the range of 5 nM to 4 μM with a very low limit of detection (LOD) of 2.88 nM. Moreover, the application feasibility of the developed CdS/rGO@Au heterojunction sensor was verified by the detection of Cu2+ in real water samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A low cost and simple method for the detection of gallic acid in food. • The g-C 3 N 4 @CNT has good chemical stability and non-toxicity. • This is a covalently bonded "signal-on" high-sensitivity non-enzyme PEC sensor. • The constructed PEC sensor has an ultra-low LOD and a wide linear range. • This is first PEC sensor based on g-C 3 N 4 @CNT heterojunction to detect gallic acid. Gallic acid (GA) is found in a wide range of natural plants and is relevant to the health of human beings. Here, a photoelectrochemical sensing platform based on g-C 3 N 4 @CNT heterojunction has been prepared for the highly sensitive and selective detection of GA. Under the light of xenon lamp, the photocurrent of g-C 3 N 4 @CNT is 7 times higher than that of g-C 3 N 4. And the sensor generates 4 times more photocurrent in the presence of GA than without GA. This sensor has a wide linear range from 10 nM to 10 μM with a limit of detection as low as 2 nM. Also, the abundant amino groups of g-C 3 N 4 provide excellent selectivity for the sensor. Furthermore, the sensor can be used for the analysis of GA in black tea samples, which provides a novel and rapid method for the detection of GA in food samples. [ABSTRACT FROM AUTHOR]