Electrochemical Sensing

About

Background: A 3D interdigitated electrode (IDE) sensor using carbon nanotube templated manufacturing (CNT-M) for highly sensitivity, rapid, and point-of-care sensing. The invention is a universal electrochemical sensor platform that can be biofunctionalized with a wide range of biorecognition agents (e.g., antibodies, aptamers/DNA, enzymes) for distinct sensing applications (e.g. cancer or MRSA – antibiotic resistant bacteria). A promising sensing technique in the detection of biomarkers is electrochemical impedance spectroscopy (EIS). EIS is capable of detecting small variations in resistance/capacitance changes due to biological agents binding to an electrical circuit and thus effectively enables label-free biosensing. Some of the first impedimetric biosensors developed in the 1980s showed tremendous promise in monitoring enzyme activity via protein adsorption and antibody/antigen binding, however, they also suffered from extremely small impedance changes that limited their sensitivity. To circumvent these issues researchers have used micro/nano-fabrication techniques to create two distinct meandering electrode arrays arranged in an interdigitated fashion. The micro/nano scale feature sizes of these interdigitated electrodes (IDEs) generate superb signal-to-noise ratios, in part due to reduced noise from the electrical double layer that can enable orders of magnitude improvement in biosensing when compared to conventional microelectrodes. In addition to sensitivity, IDE structure also offers a fast establishment of a steady state. In addition to the regular IDE geometry and hence sensing, the sensitivity, signal to noise ratio, fast steady-state establishment with better transduction of biomolecules could further be harnessed by designing IDEs with 3D finger electrodes. The impedance change is considerably affected when finger electrode dimensions and interspacing are comparable to the biomolecule length (1-100nm); if not, the effect of biomolecules will be negligible, and the measured impedance will mainly be determined by the conductivity of the solution and the double layer capacitance within the sensor/electrolyte interface. Utilizing the conventional microelectric technology, it is difficult, and time consuming, to achieve such low resolution. Thus, a 3D IDE delivers a theoretically higher detectability as compared to a planar impedimetric sensors. Possible applications include: MRSA DETECTION -- This proposal will demonstrate the utility and sensitivity limits of the 3D IDE sensors in the detection of the antibiotic-resistant bacteria, Methicillin-resistant Staphylococcus aureus (MRSA). MRSA is the leading cause of nosocomial and community-acquired infections worldwide with MRSA accounting for up to 60% of all S. aureus isolates [8, 9]. There is particular concern about the spread of livestock-associated MRSA, since it has been associated with colonization and infection of humans, particularly swine as hosts, and have been detected at all different levels of the swine production chain [10]. If not diagnosed early and treated aggressively, these human pathogens can cause a range of life-threatening illnesses, including septicemia and toxic shock syndrome [11]. The current standard microbiology agar-based methodologies for identifying MRSA from a sample culture are time consuming, often requiring 24 to 72 h. Polymerase chain reaction (PCR)-based assays for MRSA have reduced this test time, but PCR requires expensive equipment and highly trained personnel and like the agar-based MRSA test methodologies, cannot be used for in-field, real-time MRSA testing. The inability to provide rapid and definitive MRSA diagnosis delays initiation of appropriate control measures and increases the likelihood of continued transmission as well as secondary infections. Currently, there does not exist a rapid field test for MRSA. Therefore, there is a critical need to develop a simple, reliable, rapid diagnostic test for detecting strains of MRSA pathogens in livestock production samples in the field for continuous monitoring of MRSA colonization and infection. ORAL CANCER SCREENING -- This proposal will also demonstrate the potential for cancer screening through a demonstration of oral cancer detection. Cancer originating from the oral cavity or pharynx is now the sixth most common type of cancer and its incident rate is increasing [12, 13]. The five year survival rate in the U.S. for oral cancer remains at 62%—a survival rate that is substantially lower than prostate cancer (99%) and breast cancer (89%) [14] and has not significantly changed over the last 30 years despite recent advances in treatment [15]. Oral cancers are almost entirely (~90%) due to squamous cell carcinomas (OSCC) which originates in the epithelial lining of the oral cavity and can spread quickly to other parts of the body [16]. Screenings for OSCC generally involves a clinical oral examination (COE) that can be regularly administered by a dentist during routing patient visits. However, the diagnosis of OSCC based on a COE alone correlates poorly with the histological results from a biopsy due in part to the following: similarity in appearance between benign and malignant lesions, expertise of examiners, and variations of diagnoses of pathologists [17]. The inaccuracies of COEs for OSCC diagnostics, including the potential for false negatives and a high incident of false positives, have led to recent calls for more sensitive and specific adjunctive technologies to improve the accuracy of early-stage detection and diagnosis of OSCC. The key to developing a more reliable point-of-care (POC) diagnostic tool for OSCC while still maintaining the high patient comfort (non-invasive nature, no need to draw blood) and rapid results (within minutes) that are paramount for wide scale implementation, may reside in saliva-based testing to detect cancer related biomarkers (e.g, CIP2A). This requires the ability to effectively detect the low concentrations of these biomarkers in saliva.