Ultra-sensitive optical biosensor based on whispering gallery modes: The effect of buffer solutions refractive index on their sensitivity and performance

Background: Whispering gallery modes (WGM) biosensors are ultrasensitive systems that can measure amount of adsorbed layer onto the micro-cavity surface. They have many applications including protein, peptide growth, DNA and bacteria detection, molecular properties measurements and specific interaction and drug table recognitions due to their high sensitivity, compact size and label free sensing mechanism. Objective: In this paper we investigate the effect of buffer solution on detection of specific biomolecules in WGM biosensors through its refractive index change. Methods: The propagation of electromagnetic waves in a dielectric microsphere is analyzed by solving Maxwell’s equations through proper boundary condition to find a concise relation for micro-cavity resonance shift. Results: Analysis of the buffer solution’s refractive index effects on detection of BSA by WGM biosensors are presented and it was shown that even a very small change in the refractive index of buffer solution can affect the biosensor wavelength shift and the sensitivity of biosensors. Conclusion: This study opens up a discussion in biosensor sensitivity based on true and reliable performance of the buffer solution through its accurate determination of refractive index and behavior. To avoid expensive methods of enhancing sensitivity, one can improve the sensitivity of WGM biosensor to some extent, by means of using proper buffer solution.