Electrochemical Sensors Based on Screen-Printed Electrodes: The Use of Phthalocyanine Derivatives for Application in VFA Detection

Highly Sensitive Electrochemical Sensor for Diagnosis of Diabetic Ketoacidosis (DKA) by Measuring Ketone Bodies in Urine

In this report, we present an enzyme deposited Au electrode for an electrochemical measurement of acetylacetic acid (AcAc) in urine. The electrode has an immobilized layer of a mixture of D-β-hydroxybutyrate dehydrogenase (HBDH) and nicotinamide adenine dinucleotide (NADH) as sensing material to investigate its electroanalytical properties by means of cyclic voltammetry (CV). The modified electrodes are used for the detection of AcAc and present a linear current increase when the AcAc concentration increases. The electrode presents a limit of detection (LOD) of 6.25 mg/dL in the range of 6.25-100 mg/dL for investigation of clinical relevance. Finally, the electrode was evaluated using 20 patient samples. The measured results of urine ketone by the developed electrode were compared with the clinical results from a commercial kit, and the analysis showed good agreement. The proposed electrode was demonstrated to be a very promising platform as a miniaturized electrochemical analyzer for point-of-care monitoring of the critical biochemical parameters such as urine ketone.

Recent developments in monitoring technology for anaerobic digesters: A focus on bio-electrochemical systems

With the increasing popularity of waste to energy conversion, demand for large-scale operation of anaerobic digestors has emerged in the market. However, the process instabilities in anaerobic digestors limit the expansion of facilities to high loading rates. The irregularities in the process can be addressed directly by altering the feedstock characteristics provided an on-hand, robust, and sensitive monitoring device is available. In this context, the bioelectrochemical system has emerged as an excellent tool for monitoring and optimizing the anaerobic process within the reactor. This article reviews the gradual evolution in techniques and approaches for monitoring of anaerobic digestion (AD) process. An analysis of the recently popular biosensing techniques has been done with a focus on the bioelectrochemical monitoring system and its operation mode. A brief attempt to highlight the current challenges in the field of bioelectrochemical process monitoring for AD has also been made, which can be supportive of future research.

Rapid antibiotic susceptibility testing using low-cost, commercially available screen-printed electrodes

Antimicrobial resistance (AMR) is an issue of upmost global importance, with an annually increasing mortality rate and growing economic burden. Poor antimicrobial stewardship has resulted in an abundance and diverse range of antimicrobial resistance mechanisms. To tackle AMR effectively, better diagnostic tests must be developed in order to improve antibiotic stewardship and reduce the emergence of antibiotic resistant organisms. This study employs a low-cost, commercially available screen printed electrode modified with an agarose-based hydrogel deposit to monitor bacterial growth using the techniques of electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) giving rise to a new approach to measuring susceptibility. Susceptible and drug resistant Staphylococcus aureus strains were deposited onto agarose gel modified electrodes which contained clinically important antibiotics to establish growth profiles for each bacterial strain and monitor the influence of the antibiotic on bacterial growth. The results show that S. aureus is able to grow on electrodes modified with gel containing no antibiotic, but is inhibited when the gel modified electrode is seeded with antibiotic. Conversely, methicillin-resistant S. aureus (MRSA; the drug resistant strain) is able to grow on gel modified electrodes containing clinically relevant concentrations of antibiotic. Results show rapid growth profiles, with possible time to results for antibiotic susceptibility <45 min, a significant improvement on the current gold standards of at least 1-2 days.

Influence of Graphene Oxide Concentration when Fabricating an Electrochemical Biosensor for DNA Detection

We have investigated the influence exerted by the concentration of graphene oxide (GO) dispersion as a modifier for screen printed carbon electrodes (SPCEs) on the fabrication of an electrochemical biosensor to detect DNA hybridization. A new pretreatment protocol for SPCEs, involving two successive steps in order to achieve a reproducible deposition of GO, is also proposed. Aqueous GO dispersions of different concentrations (0.05, 0.1, 0.15, and 0.2 mg/mL) were first drop-cast on the SPCE substrates and then electrochemically reduced. The electrochemical properties of the modified electrodes were investigated after each modification step by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), while physicochemical characterization was performed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Finally, the sensing platform was obtained by the simple adsorption of the single-stranded DNA probe onto the electrochemically reduced GO (RGO)-modified SPCEs under optimized conditions. The hybridization was achieved by incubating the functionalized SPCEs with complementary DNA target and detected by measuring the change in the electrochemical response of [Fe(CN)6]3-/4- redox reporter in CV and EIS measurements induced by the release of the newly formed double-stranded DNA from the electrode surface. Our results showed that a higher GO concentration generated a more sensitive response towards DNA detection.

Innovative operation of microbial fuel cell-based biosensor for selective monitoring of acetate during anaerobic digestion

Volatile fatty acids (VFAs) especially acetate concentration have been proved to be a sensitive and reliable indicator for many anaerobic processes such as anaerobic digestion (AD). Microbial fuel cells (MFC) have been demonstrated as a promising VFAs sensor due to simple reactor design and operating conditions among microbial electrochemical biosensors. However, the conventional MFC biosensors may fail to distinguish between VFAs and other organics as real digestates containing complex organics and microbes are fed into anode directly. In the present study, an MFC based biosensor was developed and operated in a smart way for selective acetate detection. In the biosensor, acetate ions contained in the AD sample was first fed into the cathode, and then acetic ion transferred through the membrane from the cathode to anode chamber where it was further used as the sole substrate by pre-enriched electroactive biofilm for the current generation. A linear correlation between the current density and acetate concentrations (0.5-20 mM) at varied reaction time (1-5 h) was established. Then, the interference from propionate, butyrate, isobutyrate, and glucose on the performance of the biosensor was evaluated. Furthermore, the influence of sample temperatures (37 and 55 °C) was also studied. Finally, the VFAs content in real AD effluent with this biosensor was measured. The results corresponded well with gas chromatographic measurements. This simple, and reliable biosensor could serve as a promising alternative method for acetate detection in the AD process or any other acetate-rich fluids.

A simple sonochemical approach to fabricate a urea biosensor based on zinc phthalocyanine/graphene oxide/urease bioelectrode

A novel zinc phthalocyanine/graphene oxide (ZnPh/GO) nanocomposite modified glassy carbon electrode (GCE) was prepared by using sonochemical approach and simple drop casting method. Urease (Urs) was used as the specific enzyme for urea detection and was physically immobilized onto the surface of ZnPh/GO nanocomposite. The fabricated ZnPh/GO/Urs matrix was successfully characterized by UV-vis-spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), raman spectrum, thermogravimetric analysis, cyclic voltammetric (CV) and amperometric techniques. The electrocatalytic performance of the ZnPh/GO/Urs electrode was investigated by urea biosensor. Our results demonstrate that the modified electrode has excellent electrocatalytic activity towards the sensing of urea in 0.1 M phosphate buffer solution (PBS, pH 7.2). The biosensor tolerated a wide linear concentration range for urea from 0.4 to 22 μM (R² = 0.991), with a detection limit of 0.034 µM (S/N = 3). The ZnPh/GO/Urs bioectrode has several excellent properties, including a fast response time, high reproducibility and stability.