Fluorescence imaging immuno-assay biosensors on biological photonic crystals (Conference Presentation)

Optical biosensing has achieved remarkable levels of sensitivity and has enabled early detection of various toxins and biomarkers. Fluorescence spectroscopy is among the most common and powerful optical detection techniques, capable of single molecule detection. This is done by exciting the sample using a light source, collecting the fluorescence light inherent in the sample or on a reporter molecule, and measuring the fluorescence spectrum using a spectrometer. This modality is effective for multiplex sensing as full spectral data is acquired. However, fluorescence spectroscopy requires multiple measurements at multiple points to achieve a representative sampling of a sensor. Fluorescence imaging is a detection modality similar to fluorescence spectroscopy, but replaces the spectrometer with an imager such as a camera thus reducing cost and complexity. Imaging allows data acquisition at multiple points in a large area of your sensor in a single measurement making it a more efficient sensing method but does not acquire spectral data. Both fluorescence sensing modalities have been shown to be very powerful in pristine laboratory settings but when the equipment or measurement area are not ideal, additional enhancement is needed. This can be achieved by implementing a sensing substrate capable of enhancing fluorescence signals to practical detection levels. Diatoms are unicellular marine organisms that grow a biosilica shell called a frustule. These frustules are porous with nanostructured patterns and represent naturally occurring photonic crystals which are known to enhance excitation and emission of fluorophores. In addition to the optical enhancements of diatoms, the large surface area allows for large numbers of analytes to aggregate making fluorescence signals stronger. In this work, we employ naturally occurring photonic crystal diatoms to create a sensor capable of enhancing the fluorescence of a standard sandwich immunoassay. Using this sensor, we achieved detection down to 10-16 M using fluorescence spectroscopy and 10-15 M for fluorescence imaging. These represent a 100× and 10× enhancement for the two respective detection modalities over equivalent, non-diatom sensors. This highlights the capability of our sensor to enhance fluorescence optical signals and its potential to be used in point-of-care biosensing applications.