(85a) Point-of-Care Diagnostics: Nanostructured Materials for Electrochemical Biosensing

Authors: 
Mahshid, S. S., University of Toronto
Development of rapid approaches that are capable of in-situ and real-time monitoring of analytes in complex matrices could in principle, impact many applications including medical diagnostics, prognostics and therapeutics. Unfortunately, current methods for the quantitative detection of disease markers, such as ELISAs, Western blots, fluorescence polarization assays, are not only slow but also, complex multiple-step processes reliant on well-trained technicians working in fully-equipped laboratories. By the way, over the past two decades, many novel approaches for detection of biomarkers have been explored among which, electrochemical sensors have shown a lot of promises since they are known to be rapid, reagentless and easily multiplexed. However, given the fact that signal originates from the electron transfer, further steps need to be taken toward a specific and sensitive signal response aiming for a point-of-care platform. By engineering the sensor’s surface, we demonstrate modifications such as: (1) immobilization of selecting/capturing monolayers (DNAs and proteins) on the interface of the sensing electrode to provide the desired specificity in real biological samples, e.g. whole blood, and (2) introducing of surface nanoroughness and microscale electrodes to the sensor platform to provide direct analysis of clinical samples with appropriate target detection limits, and low levels of false negatives and false positives.

More specifically, through our newly invented signal-transduction mechanism, SHHA (steric hindrance hybridization assay), we achieved the high specificity together with sensitivity for the design of capturing monolayer toward any target of interest. SHHA is a homogenous assay, which in the electrochemical format, it takes advantage of the high affinity and specificity of a DNA strand carrying redox moiety, to hybridize to its complementary DNA strand attached to the electrode’s surface and generate electrochemical signal. This capturing mechanism also takes advantage of the dimension of a targeted macromolecule that upon binding to the DNA strand, inhibits the hybridization to the surface and reduces the electrochemical signal. In principle we are able to adapt this signaling mechanism for detection of any type of target biomolecule either individually or in multiplexing format aiming for detection of multiple analytes.

On the other hand, we achieve high sensitivities in our sensing systems through utilizing electrochemical detectors with nanostructured electrodes in macroscale and microscale. In this regard, the improvement in sensor’s selectivity is achieved through the impact of nanoroughness on the thermodynamics of surface reactions. Also, the high curvature on the nanostructures is advantageous for the display of capturing monolayer on the surface with nanoscale roughness. This provides low detection limits for the sensors down to picomolar and femtomolar. Plus, these nanostructured electrodes enhance the speed of detection mechanism by their macroscopically sized electrodes that overcomes the limitations of diffusive transport impeding the performance of nano-sized sensors.

Finally by combination of the two fields of bioengineering and materials design, we have found our way through translational research by showing the real-world application of our sensor systems. In a manner similar to the “home glucometer”, we have applied our sensor systems into the portable microelectronic-chip devices for (1) rapid diagnosis of HIV through quantitative detection of anti-HIV antibodies directly in patient samples; (2) therapeutic monitoring of digoxin drug molecule through indirect capturing of the drug molecule in blood; and (3) at-line monitoring of secreted factors in the hematopoietic stem cell culture.