Detection of vaccinia virus proteins in wastewater environment using biofunctionalized optical fiber semi-distributed FBG-assisted interferometric probes

In this work, we present the detection of proteins expressed by poxvirus with fiber-optic probes based on a semi-distributed interferometer (SDI) assisted by a fiber Bragg grating (FBG), performing the measurement directly into a wastewater sample. Modern biosafety applications benefit from real-time, dynamic-sensing technologies that can perform diagnostic tasks into a wide set of analytes, with a particular emphasis on wastewater, which appears to collect a significant number of viral titers in urban and indoor environments. The SDI/FBG probe can perform substantial progress in this field, as it embeds a dual sensitivity mechanism to refractive index changes (sensitivity up to 266.1 dB/RIU (refractive index units)) that can be exploited in biosensing, while simultaneously having the capability to measure the temperature (sensitivity 9.888 pm/°C), thus providing an intrinsic cross-sensitivity compensation. In addition, a standard FBG analyzer can be used as an interrogator, improving affordability and real-time detection over previous works. The probes have been functionalized with antibodies specific for L1, A27 and A33 vaccinia virus proteins, performing detection of a protein concentration in a scenario compatible with online viral threat detection. Direct detection of wastewater samples shows that the L1-functionalized sensor has a higher response, 9.1–11.3 times higher than A33 and A27, respectively, with a maximum response of up to 1.99 dB and excellent specificity. Dynamic detection in wastewater shows that the sensors have a response over multiple detection cycles, with a sensitivity of 0.024–0.153 dB for each 10-fold increase of concentration.