A B S T R A C TAn electrochemical sensor modified with a molecularly imprinted polymer (MIP) and carboxylfunctionalized multi-walled carbon nanotubes (MWCNT-COOH) was developed for the sensitive and selective detection of diuron in river water samples. An MIP was obtained by bulk polymerization using the best monomer (methacrylic acid) selected by computational simulation. The surface characteristics of the MIP and NIP (control polymer) samples were evaluated by means of surface area and pore volume determinations, using the BET method. The adsorption efficiency of the MIP was determined in adsorption tests that revealed high adsorption, relative to the control polymer. In addition, MWCNTs functionalized with carboxyl groups were used to enhance the performance of the sensor. Electrochemical studies of diuron using the MIP and MWCNT-COOH immobilized on a carbon paste electrode were performed with wave square voltammetry (SWV). The analytical parameters pH, buffer composition, and amounts of MWCNT-COOH and MIP were investigated and optimized. Excellent results were obtained with a linear range of between 5.2 Â 10 À8 and 1.25 Â 10 À6 mol L À1 , detection limit of 9.0 Â 10 À9 mol L À1 , and sensitivity of 5.1 Â10 5 mA L mol À1 . The MWCNT-COOH-MIP/CPE showed an enhanced electrochemical response, with sensitivity 7.9-fold greater than for a plain carbon paste electrode (CPE). Application of the sensor using river water samples resulted in recoveries between 96.1 and 99.5% and RSD <5% (n=3), demonstrating the reliability of this device.

The recent outbreak of the Zika virus (ZIKV) in the Americas and multiple studies that linked the virus to the cases of microcephaly and neurological complications have revealed the need for cost efficient and rapid ZIKV diagnostics tests. Here, a diagnostic platform relying on a four-way junction (4WJ)-based biosensor with electrochemical readout using a Universal DNA-Hairpin (UDH) probe for the selective recognition of an isothermally amplified ZIKV RNA fragment is developed. The 4WJ structure utilizes an electrode-immobilized stem-loop (DNA-hairpin) probe and two DNA adaptor strands complementary to both the stem-loop probe and the targeted fragment of a ZIKV amplicon. One of the adaptor strands is responsible for high selectivity of the target recognition, while another helps unwinding the target secondary structure. The first adaptor strand contains a redox label methylene blue to trigger the current change in response to the target-dependent formation of the 4WJ structure on the surface of the electrode. The amplicon can be analyzed directly from the amplification sample without the need for its purification. The proposed diagnostic methodology exhibits the limit of ZIKV RNA detection of 1.11 fg/μL (∼0.3 fM) and high selectivity that allows for reliable discrimination of ZIKV from West Nile virus and four dengue virus serotypes. Overall, the analysis of ZIKV RNA can be completed in less than 1 h, including amplification and electrochemical detection.

An alternative for determining environmental pollutants, like textile dyes, is the use of molecularly imprinted polymers (MIPs) as solid phase extraction (SPE) or as sensor recognition systems. MIPs are tailor-made artificial receptor sites in a polymer, which present good affinity and selectivity. This work shows the synthesis of MIPs for the Acid Green 16 (AG16) textile dye and the results of rebinding, selectivity and application of this MIP in water samples. MIP synthesis was performed using AG16 dye (template), 1-vinylimidazole (functional monomer), ethylene-glycol-dimethacrylate (cross-link), 2,2'-azobis(2-methylpropionitrile) (initiator) and methanol (solvent) by bulk synthesis. The imprinted polymer presented excellent rebinding of 83%, an imprinted factor of 6.91 and great selectivity in comparison with other textile dyes. Additionally, the MIP showed high efficiency in the extraction of this dye in water samples, presenting a recovery rate close to 100% and a better performance when compared to commercial SPE cartridges. Due to this excellent performance for AG16, the application of this MIP to determine dyes in different matrices of environmental importance is promising.

A cheap and robust method for the detection and quantification of textile dyes is the use of biomimetic sensors with optical transduction, employing a molecularly imprinted polymer (MIP) as the recognition element. This paper presents the optimization of a MIP for the dye, basic red 9 (BR9) and the immobilization of these polymers on a disposable 4-cm long polystyrene optical waveguide for the development of an evanescent wave fiber optic sensor aimed at the determination and quantification of this dye in different matrices and industrial effluents. MIPs were synthesized using 2-acrylamido-2-methyl-1-propanesulfonic acid and ethylene glycol dimethacrylate, as functional monomer and cross-linker, respectively. The polymer was then immobilized on the waveguide by dip-coating the fiber in the polymer suspension. The sensing element was interrogated with a fiber-coupled spectrophotometer. BR9 could be detected in the low M range, thus making it a promising device for determining this compound in textile effluents.