Nanobiosensor Arrays for Rapid On-Site Multiplexed Detection of Forensically Relevant Body Fluids at Crime Scenes

Forensic science heavily relies on the identification of body fluids at crime scenes. It helps validate the relevance of evidence, pinpoint the crime's location and severity, and determine which items need DNA analysis, thus optimizing costs and avoiding unnecessary tests. Traditional methods for detecting these fluids are mostly qualitative, often lacking in sensitivity and selectivity. To overcome these limitations, we have developed chemiresistive nanobiosensor arrays using single-walled carbon nanotubes (SWNTs) for quantitative, selective, rapid, on-site identification of multiple body fluids—namely blood, semen, saliva, urine, and sweat—by detecting specific protein biomarkers using corresponding antibodies. The sensor array, created via inkjet printing of silver leads on chromatography paper, requires minimal sample volume, distributed efficiently through the built-in paper microfluidics. For fabricating chemiresistors, we have developed an all-in-one style SWNT-Antibody Bio-Ink that can be drop-casted or printed on the substrate. Any specific antigen- antibody interaction near the interface of the SWNTs and environment causes a significant increase in the measured electrical responses due to surface charge-induced gating effect, which gives us our sensor response values. Our experiments demonstrated very high responses for specific interactions, even when transitioning from purified antigens to complex human samples, and very low responses for non-specific interactions, confirming the sensor's exceptional specificity. Additionally, we achieved quantitative and selective protein detection with very low limits of detection values. Beyond forensic investigations, this technology also has practical applications in medical diagnostics, environmental monitoring, and food safety. In summary, our biosensing platform holds great potential for revolutionizing crime scene investigations and fostering the use of paper-based chemiresistors in broader sensing applications.