This review article presents an overview of recent work on electrochemical biosensors developed using microfabrication processes, particularly sensors used to achieve sensitive and specific detection ...of DNA sequences. Such devices are important as they lend themselves to miniaturisation, reproducible mass-manufacture, and integration with other previously existing technologies and production methods. The review describes the current state of these biosensors, novel methods used to produce them or enhance their sensing properties, and pathways to deployment of a complete point-of-care biosensing system in a clinical setting.
•Overview of thin film electrochemical DNA sensors.•Covers methods of enhancing sensitivity, stability, and capacity for manufacture of such biosensors.•Looks at integration of biosensors in lab-on-a chip style systems.•Reviews work published on miniaturizing DNA biosensors and integrating them with CMOS technology.
Tetracycline antibiotics are used extensively in veterinary medicine, but the majority of the administrated dose is eliminated unmodified from the animal through various excretion routes including ...urine, faeces and milk. In dairy animals, limits on residues secreted in milk are strictly controlled by legislation. Tetracyclines (TCs) have metal chelation properties and form strong complexes with iron ions under acidic conditions. In this study, we exploit this property as a strategy for low cost, rapid electrochemical detection of TC residues. TC-Fe(III) complexes in a ratio of 2:1 were created in acidic conditions (pH 2.0) and electrochemically measured on plasma-treated gold electrodes modified with electrodeposited gold nanostructures. DPV measurements showed a reduction peak for the TC-Fe(III) complex that was observed at 50 mV (vs. Ag/AgCl QRE). The limit of detection in buffer media was calculated to be 345 nM and was responsive to increasing TC concentrations up to 2 mM, added to 1 mM FeCl3. Whole milk samples were processed to remove proteins and then spiked with tetracycline and Fe(III) to explore the specificity and sensitivity in a complex matrix with minimal sample preparation, under these conditions the LoD was 931 nM. These results demonstrate a route towards an easy-to-use sensor system for identification of TC in milk samples taking advantage of the metal chelating properties of this antibiotic class.
This paper outlines a simple label-free sensor system for the sensitive, real time measurement of an important protein biomarker of sepsis, using a novel microelectrode integrated onto a needle ...shaped substrate. Sepsis is a life threatening condition with a high mortality rate, which is characterised by dysregulation of the immune response following infection, leading to organ failure and cardiovascular collapse if untreated. Currently, sepsis testing is typically carried out by taking blood samples which are sent to a central laboratory for processing. Analysis times can be between 12 and 72 h making it notoriously difficult to diagnose and treat patients in a timely manner. The pathobiology of sepsis is becoming increasingly well understood and clinically relevant biomarkers are emerging, which could be used in conjunction with a biosensor to support real time diagnosis of sepsis. In this context, microelectrodes have the analytical advantages of reduced iR drop, enhanced signal to noise ratio, simplified quantification and the ability to measure in hydrodynamic situations, such as the bloodstream. In this study, arrays of eight (r = 25 µm) microelectrodes were fabricated onto needle shaped silicon substrates and electrochemically characterised in order to confirm successful sensor production and to verify whether the observed behaviour agreed with established theory. After this, the electrodes were functionalised with an antibody for interleukin-6 (IL-6) which is a protein involved in the immune response to infection and whose levels in the blood increase during progression of sepsis. The results show that IL-6 is detectable at physiologically relevant levels (pg/mL) with incubation times as short as 2.5 min. Electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) measurements were taken and DPV was concluded to be the more suitable form of measurement. In contrast to the accepted view for macro electrodes that the impedance increases upon antigen bind, we report herein a decrease in the micro electrode impedance upon binding. The small size of the fabricated devices and their needle shape make them ideal for either point of care testing or insertion into blood vessels for continuous sepsis monitoring.
•An array of 8 × 50 µm gold electrodes were fabricated onto a needle shaped substrate.•The device was electrochemically characterised to confirm successful fabrication and demonstrate microelectrode behaviour.•Interleukin 6 (IL-6) antibody was immobilised onto the electrode surface.•EIS & DPV measurements were demonstrated as effective methods for detection of antibody- antigen binding.•A dose response curve was established showing IL-6 could be measured at normal and elevated levels using DPV.
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.
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•A gold screen printed electrode modified with a hydrogel deposit was developed.•The sensor was electrochemically characterised to monitor bacterial growth.•Growth profiles were developed for susceptible and drug resistant S. aureus.•Rapid growth profiles established; antibiotic susceptibility results <45 min.
Abstract Earlier access to patients’ biomarker status could transform disease management. However, gold-standard techniques such as enzyme-linked immunosorbent assays (ELISAs) are typically not ...deployed at the point-of-care due to their cumbersome instrumentation and complexity. Electrochemical immunosensors can be disruptive in this sector with their small size and lower cost but, without further modifications, the performance of these sensors in complex media ( e.g. , blood) has been limited. This paper presents a low-cost fluidic accessory fabricated using widely accessible materials and processes for boosting sensor sensitivity through confinement of the detection media next to the electrode surface. Liquid confinement first highlighted a spontaneous reaction between the pseudoreference electrode and ELISA detection substrate 3,3’,5,5’-tetramethylbenzidine (TMB) that decreases the amount of oxTMB available for detection. Different strategies are investigated to limit this and maximize reliability. Next, flow cell integration during the signal amplification step of sensor preparation was shown to substantially enhance the detection of cytokine interleukin-6 (IL-6) with the best sensitivity boost recorded for fresh human plasma (x7 increase compared to x5.8 in purified serum and x5.5 in PBS). The flow cell requires no specialized equipment and can be seamlessly integrated with commercial sensors, making an ideal companion for electrochemical signal enhancement.
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•A flexible, thin-film carbon electrode developed for detection of dopamine.•The electrode was electrochemically characterised to assess its sensitivity.•The electrode provided a ...dopamine limit of detection of ~50 pM.•Good selectivity shown between dopamine and key interferent, ascorbic acid.
A flexible, thin-film carbon electrode is reported for detection of the key neurotransmitter dopamine using standard electroanalytical techniques of cyclic voltammetry, differential pulse voltammetry and square wave voltammetry. The thin-film electrode has been explored as a possible low-cost solution to detect low concentrations of dopamine and its performance has been compared with a commercially available screen printed carbon electrode. It was found that the thin-film electrode is more sensitive than the screen printed electrode, and can faithfully detect dopamine between 50 pM and 1 mM concentrations. The electrode provides a limit of detection of ~50 pM, displays good selectivity between dopamine and ascorbic acid, and is able to show a level of differentiation between the two compounds in terms of peak currents as well as oxidative potentials at physiologically relevant concentrations. This is in contrast to the screen printed electrode which is unable to discriminate between dopamine and ascorbic acid at the same concentrations. The key advantages of the presented electrode system are its low-cost, flexible substrate, and the ability to achieve very low levels of dopamine detection without requiring any electrode surface modification steps, a key factor in reducing fabrication costs and overall device complexity.
In this study, an implantable stereo-electroencephalography (sEEG) depth electrode was functionalised with an enzyme coating for enzyme-based biosensing of glucose and L-glutamate. This was done ...because personalised medicine could benefit from active real-time neurochemical monitoring on small spatial and temporal scales to further understand and treat neurological disorders. To achieve this, the sEEG depth electrode was characterised using cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) using several electrochemical redox mediators (potassium ferri/ferrocyanide, ruthenium hexamine chloride, and dopamine). To improve performance, the Pt sensors on the sEEG depth electrode were coated with platinum black and a crosslinked gelatin-enzyme film to enable enzymatic biosensing. This characterisation work showed that producing a useable electrode with a good electrochemical response showing the expected behaviour for a platinum electrode was possible. Coating with Pt black improved the sensitivity to H
2
O
2
over unmodified electrodes and approached that of well-defined Pt macro disc electrodes. Measured current showed good dependence on concentration, and the calibration curves report good sensitivity of 29.65 nA/cm
2
/μM for glucose and 8.05 nA/cm
2
/μM for L-glutamate with a stable, repeatable, and linear response. These findings demonstrate that existing clinical electrode devices can be adapted for combined electrochemical and electrophysiological measurement in patients and obviate the need to develop new electrodes when existing clinically approved devices and the associated knowledge can be reused. This accelerates the time to use and application of in vivo and wearable biosensing for diagnosis, treatment, and personalised medicine.
Graphical abstract
The goal of achieving enhanced diagnosis and continuous monitoring of human health has led to a vibrant, dynamic and well-funded field of research in medical sensing and biosensor technologies. The ...field has many sub-disciplines which focus on different aspects of sensor science; engaging engineers, chemists, biochemists and clinicians, often in interdisciplinary teams. The trends which dominate include the efforts to develop effective point of care tests and implantable/wearable technologies for early diagnosis and continuous monitoring. This review will outline the current state of the art in a number of relevant fields, including device engineering, chemistry, nanoscience and biomolecular detection, and suggest how these advances might be employed to develop effective systems for measuring physiology, detecting infection and monitoring biomarker status in wild animals. Special consideration is also given to the emerging threat of antimicrobial resistance and in the light of the current SARS-CoV-2 outbreak, zoonotic infections. Both of these areas involve significant crossover between animal and human health and are therefore well placed to seed technological developments with applicability to both human and animal health and, more generally, the reviewed technologies have significant potential to find use in the measurement of physiology in wild animals.
This article is part of the theme issue ‘Measuring physiology in free-living animals (Part II)’.
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