Multi-purpose optical biosensors for real-time detection of bacteria, viruses and toxins

A universal optical microchip sensing platform demonstrating real-time, label-free detection of a wide range of biological agents is presented. SpectroSens™ chips containing high-precision planar Bragg gratings are exploited as low-cost, robust refractive index sensors. Sensitivity to biological agents is conferred by functionalising the sensing surface with antibodies selected against targets of interest. Several methods for immobilisation of bio-molecules on the metal oxide-coated sensing surface have been investigated. In this study, surfaces were modified with an amino-terminated silane monolayer and activated by glutaraldehyde cross-linking for covalent attachment of recombinant Protein A/G, to which agent-specific antibodies were immobilised. Binding of target antigens (introduced under flow) to the surface-immobilised antibodies results in localised changes in refractive index; upon laser-induced interrogation of the sensing region via optical fibres, these antibody–antigen interactions manifest as increases in wavelength of light reflected from the Bragg grating. Detection of biological targets including proteins (ovalbumin < 10 nm), viruses (MS2 < 100 nm), bacterial cells (Escherichia coli > 1 μm) and spores (Bacillus atrophaeus > 1 μm) in real-time has been demonstrated. The large size range of detection targets is attributed to a large penetration depth of the sensing light of >1 μm into the sample liquid using these sensors. This multi-analyte capability enables utilisation of this sensing technology in applications ranging from bio-threat detection for defence and homeland security to point-of-care clinical diagnostics.