The as-prepared co-doped N/Ag carbon dot (CD_NAg) has strong catalysis of H₂O₂ oxidation of 3,3′-dimethylbiphenyl-4,4′-diamine (DBD). It forms an oxidation product (DBD_ox) with surface-enhanced Raman scattering (SERS) activity at 1605 cm⁻¹ in the silver nanosol substrate, and a CD_NAg catalytic amplification with SERS analytical platform can be structured based on aptamer (Apt) with the DBD oxidizing reaction. For example, the aptamer (Apt) of acetamiprid (ACT) can be adsorbed on the surface of CD_NAg, resulting in inhibited catalytic activity, the reduced generation of DBD_ox, and a weakened SERS intensity. When the target molecule ACT was added, it formed a stable Apt-ACT complex and free CD_NAg that restored catalytic activity and linearly enhanced the SERS signal. Based on this, we proposed a new quantitative SERS analysis method for the determination of 0.01–1.5 μg ACT with a detection limit of 0.006 μg/L.

Simple and facile electrochemical sensors for nitrite detection were fabricated by directly depositing ferrocenoyl cysteine conjugates Fc[CO-Cys(Trt)-OMe]₂ [Fc(Cys)₂] or Fc[CO-Glu-Cys-Gly-OH] [Fc-ECG] on screen-printed electrodes (SPEs). The modified carbon electrodes were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results indicated that Fc-ECG/SPE sensor showed enhanced current response and a lower overpotential than Fc(Cys)₂/SPE sensor for nitrite detection. Optimal operating conditions were estimated for nitrite detection by DPV. The concentration of nitrite showed a good linear relationship with the current response in the range of 1.0–50 μmol·L⁻¹ and with 0.3 μmol·L⁻¹ as the concentration for limit of detection. There were no interferences from most common ions. The development of this electrochemical sensor was used for nitrite detection in pickled juice with a R.S.D. lower than 2.1% and average recovery lower than 101.5%, which indicated that disposable electrochemical sensor system can be applied for rapid and precise nitrite detection in foods.

Quercetin (Qu) is one of the most abundant flavonoids in the human diet. High concentrations of Qu can easily cause adverse effects and induce inflammation, joint pain and stiffness. In this study, Heme was used as a sensitive element and deposited and formed nanorods on a glassy carbon electrode (GCE) for the detection of Qu. The Heme/GCE sensor was characterized using scanning electron microscopy (SEM), cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques. Under optimized conditions, the developed sensor presented a linear concentration ranging from 0.1 to 700 μmol·L⁻¹ according to the CV and DPV methods. The detection limit for the sensor was 0.134 μmol·L⁻¹ and its sensitivity was 0.12 μA·μM⁻¹·cm⁻², which were obtained from CV analysis. Through DPV analysis we obtained a detection limit of 0.063 μmol·L⁻¹ and a sensitivity of 0.09 μA·μM⁻¹·cm⁻². Finally, this sensor was used to detect the Qu concentration in loquat leaf powder extract, with recovery between 98.55–102.89% and total R.S.D. lower than 3.70%. The constructed electrochemical sensor showed good anti-interference, repeatability and stability, indicating that it is also usable for the rapid detection of Qu in actual samples.