A molecularly imprinted polymer based on multiwalled carbon nanotubes for separation and spectrophotometric determination of L-cysteine

Detection of L-cysteine in urine samples based on CdS/TiO2-modified extended-gate field-effect transistor photoelectrochemical sensor

A novel extended-gate field-effect transistor (FET) photoelectrochemical (EGFET PEC) sensor was designed for highly sensitive detection of L-cysteine (L-Cys). TiO2 was initially modified on the ITO electrode by the sol-gel dip-coating method and calcined to produce TiO2/ITO. Then, CdS was synthesized on the TiO2 surface by hydrothermal method to obtain the CdS-TiO2 heterojunction material. CdS/TiO2/ITO was connected to the gate of the FET to obtain an EGFET PEC sensor. Under the irradiation of a xenon lamp simulating visible light, the CdS/TiO2 heterojunction composite absorbs light energy to produce photogenerated electron-hole pairs, which have strong photocatalytic oxidation activity and oxidize L-Cys covalently identified by Cd(II) through CdS covalent. These pairs generate a photovoltage that controls the current between the source and the drain to detect L-Cys. Under the optimized experimental conditions, the optical drain current (ID) of the sensor exhibited a good linear relationship with the logarithm of L-Cys in the range of 5.0 × 10-9-1.0 × 10-6 mol/L, and the detection limit was 1.3 × 10-9 mol/L (S/N = 3), which is lower than the values reported by other detection methods. Results showed that the CdS/TiO2/ITO EGFET PEC sensor revealed high sensitivity and good selectivity. The sensor has been used to determine L-Cys in urine samples.

Molecularly Imprinted Polymer-Amyloid Fibril-Based Electrochemical Biosensor for Ultrasensitive Detection of Tryptophan

A tryptophan (Trp) sensor was investigated based on electrochemical impedance spectroscopy (EIS) of a molecularly imprinted polymer on a lysozyme amyloid fibril (MIP-AF). The MIP-AF was composed of aniline as a monomer chemically polymerized in the presence of a Trp template molecule onto the AF surface. After extracting the template molecule, the MIP-AF had cavities with a high affinity for the Trp molecules. The obtained MIP-AF demonstrated rapid Trp adsorption and substantial binding capacity (50 µM mg⁻¹). Trp determination was studied using non-Faradaic EIS by drop drying the MIP-AF on the working electrode of a screen-printed electrode. The MIP-AF provided a large linear range (10 pM–80 µM), a low detection limit (8 pM), and high selectivity for Trp determination. Furthermore, the proposed method also indicates that the MIP-AF can be used to determine Trp in real samples such as milk and cancer cell media.

Design of a pseudo stir bar sorptive extraction using graphenized pencil lead as the base of the molecularly imprinted polymer for extraction of nabumetone

Molecularly imprinted polymer (MIP) was synthesized through the coprecipitation method on the graphene oxide anchored pencil lead as a substrate for the first time and applied as an efficient sorbent for pseudo stir bar sorptive extraction of nabumetone. The extracted analyte was determined by a novel spectrophotometric method based on the aggregation of silicate sol-gel stabilized silver nanoparticles in the presence of the analyte. The synthesized polymer was characterized using Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Optimization of important parameters affecting the extraction efficiency was done using central composite design whereas the spectrophotometric method was optimized via one at a time variable. Under the optimal conditions, the calibration curve exhibited linearity in the concentration range of 1.5-20.0 μg L^-1. A limit of detection of 0.20 μg L^-1, an enhancement factor of 393 and relative standard deviations (at 10 μg L^-1, n = 6) of 4.6% and 8.1% for intra- and inter-day analysis were obtained. The developed procedure was successfully utilized for the quantification of traces of nabumetone in tap water and biological samples with the complex matrix including human urine and serum.

Synthesis of Fe3O4 nanobead-functionalized 8-hydroxyquinoline sulfonic acid supported by an ion-imprinted biopolymer as a recognition site for Al3+ ions: estimation in human serum and water samples

A selective and sensitive approach for the analysis of Al³⁺ in real samples using solid phase extraction combined with an ion imprinting biopolymer strategy.