Highly sensitive amperometric detection of drugs and antioxidants on non-functionalized multi-walled carbon nanotubes: Effect of metallic impurities?

A novel molecularly imprinted electrochemical sensor for the ultrasensitive detection of tert-butylhydroquinone in edible oils

Tert-butylhydroquinone (TBHQ) is widely used to increase the stability of food products; however, it is considered to be a highly unsafe preservative ingredient that has caused serious damage to human health. Thus, in this paper, a novel molecularly imprinted electrochemical sensor was designed for ultrasensitive, and selective detection of TBHQ in edible oils. The sensor was based on the molecularly imprinted polymer (MIP) synthesized with multiwalled carbon nanotube (MWCNT), and gold nanoparticle (GNP), as the coating materials, o-phenylenediamine (o-PDA) as the functional monomer, and TBHQ as the template molecule. The electrochemical behavior of MIP/GNP/MWCNT/GCE was studied using several electrochemical methods, which showed a low detection limit of 5 nM. Furthermore the sensor demostrated excellent stability, selectivity, repeatability, and reproducibility. It was successfully used to detect TBHQ in edible oils, with recoveries ranging from 98.44% to 102.09% and relative standard deviations (RSDs) of less than 2.16%, indicating that TBHQ detection in actual samples is both possible and accurate.

Batch injection analysis in tandem with electrochemical detection: the recent trends and an overview of the latest applications (2015–2020)

The purpose of the proposed review is to refer the contemporary capability of automated analytical systems, in particular batch injection analysis (BIA) in connection with electrochemical detection, for widespread applications in analytical chemistry. This combination recently represents an efficient tool for improvement of method parameters, such as speed, selectivity, and sampling rate for sensing of miscellaneous organic and inorganic substances. The review is focused on conception and usage of BIA in tandem with electrochemical detection utilizing various techniques, namely amperometry, voltammetry, and multiple pulse amperometry, as well as design of electrochemical cells constructed for BIA systems is discussed. Finally, this paper also summarizes the comprehensive overview of works published from 2015 to 2020 dealing with the electrochemical determination of different analytes by BIA in various matrices.

A Molecularly Imprinted Sol-Gel Electrochemical Sensor for Naloxone Determination

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide (ITO) electrode. The sol-gel layer was obtained from acid catalyzed hydrolysis and condensation of a solution composed of triethoxyphenylsilane (TEPS) and tetraethoxysilane (TES). The fabrication, structure and properties of the sensing material were characterized via scanning electron microscopy, spectroscopy and electrochemical techniques. Parameters affecting the sensor's performance were evaluated and optimized. A sensor fabricated under the optimized conditions responded linearly between 0.0 µM and 12 µM NLX, with a detection limit of 0.02 µM. The sensor also showed good run-to-run repeatability and batch-to-batch performance reproducibility with relative standard deviations (RSD) of 2.5-7.8% (n = 3) and 9.2% (n = 4), respectively. The developed sensor displayed excellent selectivity towards NLX compared to structurally similar compounds (codeine, fentanyl, naltrexone and noroxymorphone), and was successfully used to measure NLX in synthetic urine samples yielding recoveries greater than 88%.

Response surface methodology optimized electrochemical DNA biosensor based on HAPNPTs/PPY/MWCNTs nanocomposite for detecting Mycobacterium tuberculosis

An important issue in the prognosis of tuberculosis (TB) is a short period between correct diagnosis and start the suitable antibiotic therapy. So, a rapid and valid method for detection of Mycobacterium tuberculosis (M. tb) complex is considered as a necessity. Herein, a rapid, low-cost, and PCR-free DNA biosensor was developed based on multi-walled carbon nanotubes (MWCNTs), polypyrrole (PPy), and hydroxyapatite nanoparticles (HAPNPs) for highly sensitive and specific recognition of M.tb. The biosensor consisted of M.tb ssDNA probe covalently attached to the HANPs/PPy/MWCNTs/GCE surface that hybridized to a complementary target sequence to form a duplex DNA. The M.tb target recognition was based on the oxidation signal of the electroactive Methylene Blue (MB) on the surface of the modified GCE using differential pulse voltammetry (DPV) method. It is worth to mention that for the first time Plackett-Burman (PB) screening design and response surface method (RSM) based on central composite design (CCD) was applied as a powerful and an efficient approach to find optimal conditions for maximum M.tb biosensor performance leading to simplicity and rapidity of operation. The proposed DNA biosensor exhibits a wide detection range from 0.25 to 200.0 nM with a low detection limit of 0.141 nM. The performance of designed biosensor for clinical diagnosis and practical applications was revealed through hybridization between DNA probe-modified GCE and extracted DNA from sputum clinical samples.

Electrochemical synthesis of Prussian blue from iron impurities in 3D-printed graphene electrodes: Amperometric sensing platform for hydrogen peroxide

This communication shows the electrochemical synthesis of Prussian blue (PB) films on additive manufactured (3D-printed) electrodes from iron impurities found at the graphene-polylactic acid (G/PLA) substrate and its application as a highly selective sensor for H₂O₂. The 3D-printed G/PLA electrode was immersed in dimethylformamide for 30 min to exposure the iron impurities within the PLA matrix. Next, cyclic voltammograms (200 cycles) in the presence of potassium ferricyanide in 0.1 mol L^-1 KCl + 0.01 mol L^-1 HCl were performed to grow the PB films. The sensing properties of this novel PB/G/PLA platform were evaluated for the amperometric detection of H₂O₂ using batch-injection analysis, with a limit of detection of 0.56 μmol L^-1 under the application of 0.0 V (vs Ag/AgCl/KCl_sat.). The applicability of the sensor was demonstrated for the analysis of milk samples (10-fold diluted in the supporting electrolyte), resulting in proper recovery values (94-101%).

Determination of inorganic contaminants in carbon nanotubes by plasma-based techniques: Overcoming the limitations of sample preparation

In this work, sample preparation of carbon nanotubes (CNTs) for further determination of inorganic contaminants was investigated using a microwave-assisted wet digestion single reaction chamber system (MAWD-SRC). Analytes (Al, As, Ca, Cd, Co, Cr, Fe, La, Mg, Mo, Ni, Pb and Zn) were determined in CNTs by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS, except for Al, Ca, Fe and Mg). Method parameters were evaluated, as the mass of CNT (25-300 mg), the temperature (220-270 °C) and the time (35-75 min) of irradiation program. The accuracy was evaluated by using a certified reference material (CRM) of CNT and also by comparison of the results with those obtained using neutron activation analysis (NAA) and high resolution continuum source graphite furnace atomic absorption spectrometry with direct solid sampling (DSS-HR-CS-GF AAS). Quantitative recoveries for all elements were obtained using 275 mg of CNTs, 6 mL of 14.4 mol L^-1 HNO₃ and 0.5 mL of 30% H₂O₂ with an irradiation program of 65 min (35 min at 270 °C). No statistical difference was observed between the results obtained after the decomposition of CNTs by MAWD-SRC with those obtained by NAA and DSS-HR-CS-GF AAS. No difference was also observed for the results using the proposed method and the values for the CRM of CNT. The use of MAWD-SRC showed good performance for CNTs digestion using relatively high sample mass (up to 275 mg), contributing to low limits of quantification (LOQs) and overcoming the current limitations of sample preparation. To the best knowledge of the authors, this work reports the highest sample mass feasible to be decomposed using wet digestion for CNTs among the methods proposed in literature.

3D printing for electroanalysis: From multiuse electrochemical cells to sensors

This work presents potential applications of low-cost fused deposition modeling 3D-printers to fabricate multiuse 3D-printed electrochemical cells for flow or batch measurements as well as the 3D-printing of electrochemical sensing platforms. Electrochemical cells and sensors were printed with acrylonitrile butadiene styrene (ABS) and conductive graphene-doped polylactic acid (G-PLA) filaments, respectively. The overall printing operation time and estimated cost per cell were 6 h and $ 6.00, respectively, while the sensors were printed within minutes (16 sensor strips of 1 × 2 cm in 10 min at a cost of $ 1.00 each sensor). The cell performance is demonstrated for the amperometric detection of tert-butylhydroquinone, dipyrone, dopamine and diclofenac by flow-injection analysis (FIA) and batch-injection analysis (BIA) using different working electrodes, including the proposed 3D-printed sensor, which presented comparable electroanalytical performance with other carbon-based electrodes (LOD of 0.1 μmol L^-1 for dopamine). Raman spectroscopy and scanning electron microscopy of the 3D-printed sensor indicated the presence of graphene nanoribbons within the polymeric matrix. Electrochemical impedance spectroscopy and heterogeneous electron transfer constants (k₀) for the redox probe Ru(NH₃)₆⁺³ revealed that a glassy-carbon electrode presented faster electron transfer rates than the 3D-printed sensor; however, the latter presented lower LOD values for dopamine and catechol probably due to oxygenated functional groups at the G-PLA surface.