Enhanced electrochemical detection of cardiovascular biomarker proteins using biogenic nanoporous silica diatoms

The goal of our research is to demonstrate the feasibility of employing biogenic nanoporous silica as a key component in developing a biosensor platform for rapid label-free electrochemical detection of proteins from pure and commercial human serum samples with high sensitivity and selectivity. The biosensor platform consists of a silicon chip with an array of gold electrodes forming multiple sensor sites and works on the principle of electrochemical impedance spectroscopy. Each sensor site is overlaid with a biogenic nanoporous silica membrane that forms a high density of nanowells on top of each electrode. The biosensor performance was tested for C-reactive protein from phosphate buffered saline and human serum. The performance of the biogenic silica membrane biosensor was tested both in the presence and absence of electrophoretic immobilization. Significant enhancement in the sensitivity and selectivity was achieved with the biogenic silica biosensor for detecting C-reactive protein from both pure and human serum samples. Significant enhancements in the measured impedance signal was obtained with the application of electrophoretic immobilization The sensitivity of the biogenic silica biosensor is ~1 pg/mL and the linear dose response is observed over a large dynamic range from 1 pg/mL to 1 μg/mL.

I. Introduction

ELECTRICAL detection of protein biomarkers is a relatively new approach that monitors a specific electrical parameter that undergoes change during the protein detection event. The advent of nanotechnology in the field of clinical diagnostics has resulted in the incorporation of nanoscale materials in designing diagnostics assays, especially for electrical detection. The major classes of nanomaterials that have been used for protein biomarker detection are: nanotubes, nanowires, nanoparticles and nanotemplates [1], [2]. Often these materials have been utilized for their enhanced surface area towards developing detectors with enhanced sensitivity and reduced use of reagents. The use of carbon nanotubes for cancer protein biomarker detection has been demonstrated [3]. Electrochemical conductance technique has yielded sensitivity in the range of lower nanogram/mL (ng/mL) to a few hundred pg/mL [4]. Implementation of the field effect transistor based transconductance technique using silicon nanowires has made it possible to detect proteins with sensitivity in the range of picogram/mL-femtogram/mL [5]. The use of antibody-coated nanoparticles as electrical biosensors operating on electrochemical conductance technique has also resulted in sensitivities in the pg/mL range [4]. The use of silicon nanoporous templates for protein detection has been demonstrated with sensitivity in pg/mL [6]. In all the nanomaterial based electrical protein biosensors, detection response is on the order of minutes with very low sample volume, typically on the order of nanoliters. Among the four nanomaterial classes mentioned above, nanotemplates can be most easily configured to generate a proteomic assay similar in geometrical configuration to the ELISA assay and this has led to the design of nano template based electrical biosensor assays.