A ratiometric electrochemical sensor for detecting lead in fish based on the synergy of semi-complementary aptamer pairs and Ag nanowires@zeolitic imidazolate framework-8.

This work describes the synergistic application of semi-complementary aptamer pairs and signals on-off ratio strategies on glassy carbon electrodes (GCE) for detecting lead ions (Pb2+) in fish. Gold nanoparticles (AuPNs) as the electrode substrate can provide added binding sites for the aptamers and improve the conductivity of the electrodes. Pb2+ aptamers containing ferrocene (Fc) molecules act as molecular recognizers in the sensing system. In the presence of target ions, Fc signals are affected by conformational changes of the aptamer. The "Ag nanowires@zeolitic imidazolate framework-8 with methylene blue (AgNWs@ZIF-8/MB)" can be semi-complementary to the Pb2+ aptamer after binding to single-stranded DNA (S1). However, S1/AgNWs@ZIF-8/MB self-assembled with Pb2+ aptamer (Apt) by hybridization incubation was quickly replaced by Pb2+ competitively, resulting in the loss of methylene blue (MB) signaling molecules. Hence, the internal reference signal (MB) and conformation change signal (Fc) comprise the ratio sensing system well. Morphology, spectroscopy, and electrochemistry methods have validated the modification and sensing behaviors. The used Apt has made considerable progress in analytical performance. In interference studies and stability checks, the ratio measurement signal IFc/IMB is a more reliable signal than the single signal readout. Following a log-linear relationship, this sensor provides a wide linear range. Furthermore, the proposed sensor can be used to determine Pb2+ in fish samples, and the results agree with those obtained using ICP-MS and recovery tests.

Flexible-fabricated sensor module with programmable magnetic actuators coupled to L-cysteine functionalized Ag@Fe3O4 complexes for Cu2+ detection in fish tissues.

Heavy metal contamination for seafood, particularly fish, is arising great concerns, and consequentially it is necessary to develop a simple and direct detection method. In this work, Ag@Fe3O4 is successfully prepared by simple solvothermal method, and we present a flexible-fabricated sensor module with assembled programmable magnetic actuators. The resulting sensor integrates a three-electrode system with two programmable magnetic actuators at the bottom of the device, which regulates the amount of current by adjusting the brake to control the adsorption force and vibration. The L-Cysteine functionalized Ag@Fe3O4 is coated on the surface of the electrode, then the Cu2+ is dropped into the reaction tank. Its performance is studied by cyclic voltammetry and electrochemical impedance spectroscopy, and the key experimental conditions such as deposition potential, deposition time, and electrolyte pH are gradually optimized. Under optimal conditions, Cu2+ can be detected over a wide linear range (0.01 ~ 4 µM) and at a low LOD (0.34 nM). The results show that the proposed method has a good application prospect in the detection of Cu2+. This method is successfully applied to Cu2+ analysis in fish samples with an acceptable recovery of 93 ~ 102%.

Detection of carbendazim in oranges with metal grating integrated microfluidic sensor in terahertz.

A novel microfluidic metal grating integrated terahertz sensor has been designed, which is composed of a metal microstructure array-dielectric layer-metal layer, where the dielectric layer is the microfluidic channel carrying the analyte. By adjusting the structural parameters of the metal grating sensor, a highly confined electromagnetic field can be obtained in the microfluidic channel, thereby significantly enhancing the interaction between the analyte and the terahertz wave and improving the terahertz detection sensitivity. The metal grating described in this paper is composed of an array of square holes, which is manufactured using laser micromachining technology, so that the measurement method is simplified and improved. The results show that the addition of different concentrations of carbendazim solution resulted in a redshift of the overall spectrum, with the highest sensitivity reaching 8.773 GHz/mg L-1, which is about eight times more sensitive than the traditional terahertz transmission sensor. The relative error of using this method to determine carbendazim levels in orange juice samples was less than 5.3%. The terahertz time-domain spectroscopy technology combined with the metal grating integrated microfluidic sensor can improve the sensitivity of sample detection and realize the rapid detection and analysis of trace elements.

A signal on-off ratiometric electrochemical sensor coupled with a molecular imprinted polymer for selective and stable determination of imidacloprid.

This work presents a signal on-off ratiometric electrochemical sensor coupled with a molecular imprinted polymer (MIP) for imidacloprid (IMI) determination. The ratiometric strategy corrects the detection results by setting 6-(Ferrocenyl)hexanethiol (FcHT) as an internal reference. The MIP membrane, as a molecular recognition receptor, has a three-dimensional structure and is complementary in the shape and chemical functionality to the template. The combination of a ratiometric strategy and MIP improves the sensitivity and selectivity of the sensors. The experimental parameters, such as monomer/template ratio, electropolymerization cycle and adsorption time, are optimized to improve the IMI sensing performance of the as-fabricated electrode. Under optimal electrochemical conditions, the proposed sensor is used to detect IMI in laboratory and real samples. In a range as wide as 5 × 10-7-1 × 10-4 mol L-1, a linear relationship is well established, and the value of the correlation coefficient is 0.9984. The limit of detection (LOD, S/N = 3) is well defined as 4.7 × 10-8 mol L-1. The recovery rates range from 97.4% to 103.5% while testing real samples. The fabricated electrode shows superior anti-interference ability for IMI determination in the presence of analogs at a higher level.