A label-free optical biosensor based on nanoporous anodic alumina for tumour necrosis factor-alpha detection in chronic wounds

Tumour necrosis factor-alpha (TNF-α) is a pro-inflammatory cytokine important to wound healing. In non-healing wounds, it has been suggested that the expression of TNF-α is prolonged and elevated which contributes to impaired healing responses. Hence it is of great interest to develop biosensors towards the detection of TNF-α in non-healing wounds. In this study, we have developed a label-free optical TNF-α biosensor based on interferometric reflectance spectroscopy (IRS) technique using a functionalized nanoporous anodic alumina (NAA) thin film transducer. The biosensor is fabricated by functionalizing NAA pore walls with anti-TNF-α antibodies using silanization chemistry. Binding of TNF-α to the bioreceptors within the pores causes a change in effective optical thickness (EOT) of the NAA thin film. Thus, analyte detection is achieved by monitoring EOT evolution with time. Label-free detection of TNF-α was demonstrated in buffer solution and in complex media such as simulated wound fluid. A limit of detection of 0.13 μg/mL was achieved. This study provides proof-of-concept evidence which sets foundations for further development of biosensors as point-of-care (POC) diagnostic tools for chronic wound care.