A Universal Electrode Approach for Automated Electrochemical Molecular Analyses

Bi-ECDAQ: An electrochemical dual-immuno-biosensor accompanied by a customized bi-potentiostat for clinical detection of SARS-CoV-2 Nucleocapsid proteins

Multiplex electrochemical biosensors have been used for eliminating the matrix effect in complex bodily fluids or enabling the detection of two or more bioanalytes, overall resulting in more sensitive assays and accurate diagnostics. Many electrochemical biosensors lack reliable and low-cost multiplexing to meet the requirements of point-of-care detection due to either limited functional biosensors for multi-electrode detection or incompatible readout systems. We developed a new dual electrochemical biosensing unit accompanied by a customized potentiostat to address the unmet need for point-of-care multi-electrode electrochemical biosensing. The two-working electrode system was developed using screen-printing of a carboxyl-rich nanomaterial containing ink, with both working electrodes offering active sites for recognition of bioanalytes. The low-cost bi-potentiostat system (∼$80) was developed and customized specifically to the bi-electrode design and used for rapid, repeatable, and accurate measurement of electrochemical impedance spectroscopy signals from the dual biosensor. This binary electrochemical data acquisition (Bi-ECDAQ) system accurately and selectively detected SARS-CoV-2 Nucleocapsid protein (N-protein) in both spiked samples and clinical nasopharyngeal swab samples of COVID-19 patients within 30 min. The two working electrodes offered the limit of detection of 116 fg/mL and 150 fg/mL, respectively, with the dynamic detection range of 1-10,000 pg/mL and the sensitivity range of 2744-2936 Ω mL/pg.mm2 for the detection of N-protein. The potentiostat performed comparable or better than commercial Autolab potentiostats while it is significantly lower cost. The open-source Bi-ECDAQ presents a customizable and flexible approach towards addressing the need for rapid and accurate point-of-care electrochemical biosensors for the rapid detection of various diseases.

Non-Invasive Electrochemical Biosensors Operating in Human Physiological Fluids

Non-invasive healthcare technologies are an important part of research and development nowadays due to the low cost and convenience offered to both healthcare receivers and providers. This work overviews the recent advances in the field of non-invasive electrochemical biosensors operating in secreted human physiological fluids, viz. tears, sweat, saliva, and urine. Described electrochemical devices are based on different electrochemical techniques, viz. amperometry, coulometry, cyclic voltammetry, and impedance spectroscopy. Challenges that confront researchers in this exciting area and key requirements for biodevices are discussed. It is concluded that the field of non-invasive sensing of biomarkers in bodily fluid is highly convoluted. Nonetheless, if the drawbacks are appropriately addressed, and the pitfalls are adroitly circumvented, the approach will most certainly disrupt current clinical and self-monitoring practices.

Microfabricated electrochemical sensing devices

Electrochemistry provides possibilities to realize smart microdevices of the next generation with high functionalities. Electrodes, which constitute major components of electrochemical devices, can be formed by various microfabrication techniques, and integration of the same (or different) components for that purpose is not difficult. Merging this technique with microfluidics can further expand the areas of application of the resultant devices. To augment the development of next generation devices, it will be beneficial to review recent technological trends in this field and clarify the directions required for moving forward. Even when limiting the discussion to electrochemical microdevices, a variety of useful techniques should be considered. Therefore, in this review, we attempted to provide an overview of all relevant techniques in this context in the hope that it can provide useful comprehensive information.

Diffusion-reaction kinetics of microfluidic amperometric biosensors

Amperometric biosensors are widely applied for rapid biomarker detection in physiological and environmental samples. The dynamics and linearity of the current signal, however, are only partially understood. This study investigates the diffusion-reaction kinetics of amperometric biosensing using a self-assembled monolayer (SAM) based biosensor for bacterial 16S rRNA. A numerical model is developed to optimize the chamber dimensions and elucidate the concentration dependences of the biosensor. The results revealed that depletion of substrates associated with the chamber dimension can limit the current signal in a target concentration dependent manner. This study provides practical guidelines in the design and interpretation of microfluidic amperometric biosensors for biochemical applications.

New and developing diagnostic technologies for urinary tract infections

Timely and accurate identification and determination of the antimicrobial susceptibility of uropathogens is central to the management of UTIs. Urine dipsticks are fast and amenable to point-of-care testing, but do not have adequate diagnostic accuracy or provide microbiological diagnosis. Urine culture with antimicrobial susceptibility testing takes 2-3 days and requires a clinical laboratory. The common use of empirical antibiotics has contributed to the rise of multidrug-resistant organisms, reducing treatment options and increasing costs. In addition to improved antimicrobial stewardship and the development of new antimicrobials, novel diagnostics are needed for timely microbial identification and determination of antimicrobial susceptibilities. New diagnostic platforms, including nucleic acid tests and mass spectrometry, have been approved for clinical use and have improved the speed and accuracy of pathogen identification from primary cultures. Optimization for direct urine testing would reduce the time to diagnosis, yet these technologies do not provide comprehensive information on antimicrobial susceptibility. Emerging technologies including biosensors, microfluidics, and other integrated platforms could improve UTI diagnosis via direct pathogen detection from urine samples, rapid antimicrobial susceptibility testing, and point-of-care testing. Successful development and implementation of these technologies has the potential to usher in an era of precision medicine to improve patient care and public health.

Long-range electrothermal fluid motion in microfluidic systems

AC electrothermal flow (ACEF) is the fluid motion created as a result of Joule heating induced temperature gradients. ACEF is capable of performing major microfluidic operations, such as pumping, mixing, concentration, separation and assay enhancement, and is effective in biological samples with a wide range of electrical conductivity. Here, we report long-range fluid motion induced by ACEF, which creates centimeter-scale vortices. The long-range fluid motion displays a strong voltage dependence and is suppressed in microchannels with a characteristic length below ~300 μm. An extended computational model of ACEF, which considers the effects of the density gradient and temperature-dependent parameters, is developed and compared experimentally by particle image velocimetry. The model captures the essence of ACEF in a wide range of channel dimensions and operating conditions. The combined experimental and computational study reveals the essential roles of buoyancy, temperature rise, and associated changes in material properties in the formation of the long-range fluid motion. Our results provide critical information for the design and modeling of ACEF based microfluidic systems toward various bioanalytical applications.

A Multiplex Electrochemical Biosensor for Bloodstream Infection Diagnosis

Accurate and timely detection of bacterial pathogens will improve the clinical management of infections. Herein, we demonstrate an electrochemical biosensor that directly detects bacteria in human blood samples, resulting in the rapid diagnosis of a bloodstream infection. The multiplex biosensor detects the species-specific sequences of the 16S ribosomal RNA of bacteria for pathogen identification in physiological samples without preamplification. The analytical performance characteristics of the biosensor, including the limit of detection and probe cross-reactivity, are evaluated systematically. The feasibility of the biosensor for a diagnosis of a bloodstream infection is demonstrated by identifying bacterial clinical isolates spiked in whole blood and blood culture samples that were tested positive for bacteria. The electrochemical biosensor correctly identifies all the species in the samples with 100% concordance to microbiological analysis.

Label- and amplification-free electrochemical detection of bacterial ribosomal RNA

Current approaches to molecular diagnostics rely heavily on PCR amplification and optical detection methods which have restrictions when applied to point of care (POC) applications. Herein we describe the development of a label-free and amplification-free method of pathogen detection applied to Escherichia coli which overcomes the bottleneck of complex sample preparation and has the potential to be implemented as a rapid, cost effective test suitable for point of care use. Ribosomal RNA is naturally amplified in bacterial cells, which makes it a promising target for sensitive detection without the necessity for prior in vitro amplification. Using fluorescent microarray methods with rRNA targets from a range of pathogens, an optimal probe was selected from a pool of probe candidates identified in silico. The specificity of probes was investigated on DNA microarray using fluorescently labeled 16S rRNA target. The probe yielding highest specificity performance was evaluated in terms of sensitivity and a LOD of 20 pM was achieved on fluorescent glass microarray. This probe was transferred to an EIS end point format and specificity which correlated to microarray data was demonstrated. Excellent sensitivity was facilitated by the use of uncharged PNA probes and large 16S rRNA target and investigations resulted in an LOD of 50 pM. An alternative kinetic EIS assay format was demonstrated with which rRNA could be detected in a species specific manner within 10-40min at room temperature without wash steps.

AC Electrokinetics of Physiological Fluids for Biomedical Applications

Alternating current (AC) electrokinetics is a collection of processes for manipulating bulk fluid mass and embedded objects with AC electric fields. The ability of AC electrokinetics to implement the major microfluidic operations, such as pumping, mixing, concentration, and separation, makes it possible to develop integrated systems for clinical diagnostics in nontraditional health care settings. The high conductivity of physiological fluids presents new challenges and opportunities for AC electrokinetics-based diagnostic systems. In this review, AC electrokinetic phenomena in conductive physiological fluids are described followed by a review of the basic microfluidic operations and the recent biomedical applications of AC electrokinetics. The future prospects of AC electrokinetics for clinical diagnostics are presented.

Protein Microarrays with Novel Microfluidic Methods: Current Advances

Microfluidic-based micromosaic technology has allowed the pattering of recognition elements in restricted micrometer scale areas with high precision. This controlled patterning enabled the development of highly multiplexed arrays multiple analyte detection. This arraying technology was first introduced in the beginning of 2001 and holds tremendous potential to revolutionize microarray development and analyte detection. Later, several microfluidic methods were developed for microarray application. In this review we discuss these novel methods and approaches which leverage the property of microfluidic technologies to significantly improve various physical aspects of microarray technology, such as enhanced imprinting homogeneity, stability of the immobilized biomolecules, decreasing assay times, and reduction of the costs and of the bulky instrumentation.

Advances and challenges in biosensor-based diagnosis of infectious diseases

Rapid diagnosis of infectious diseases and timely initiation of appropriate treatment are critical determinants that promote optimal clinical outcomes and general public health. Conventional in vitro diagnostics for infectious diseases are time-consuming and require centralized laboratories, experienced personnel and bulky equipment. Recent advances in biosensor technologies have potential to deliver point-of-care diagnostics that match or surpass conventional standards in regards to time, accuracy and cost. Broadly classified as either label-free or labeled, modern biosensors exploit micro- and nanofabrication technologies and diverse sensing strategies including optical, electrical and mechanical transducers. Despite clinical need, translation of biosensors from research laboratories to clinical applications has remained limited to a few notable examples, such as the glucose sensor. Challenges to be overcome include sample preparation, matrix effects and system integration. We review the advances of biosensors for infectious disease diagnostics and discuss the critical challenges that need to be overcome in order to implement integrated diagnostic biosensors in real world settings.