Label-Free in-Situ Detection for DNA Hybridization Employing Grapefruit-Microstructured-Optical-Fiber-Based Microfluidic Whispering Gallery Mode Resonator.

A whispering gallery mode (WGM) microre- sonator based on grapefruit microstructured optical fibers (MOFs) is proposed for in-situ DNA biosensing. The MOF microresonator has a porous structure that offers natural microfluidic channels to load microfluidic samples of volume down to $100~\mu \text{L}$. Moreover, the WGM mechanism greatly enhances the interaction between WGM light and liquid sample kept inside the microcavity. The inner surface of the microcavity is functionalized with poly-L-lysine monolayer to achieve label-free binding of the single-strand probe DNA (ssDNA) through electrostatic force, and the probe immobilization as well as DNA hybridization processes are monitored in real time. The linear fitting of resonance wavelength shift versus DNA concentration in logarithmic scale indicates that DNA detection is available from 0.01 fmol/ $\mu \text{L}$ to 100 fmol/ $\mu \text{L}$. The proposed WGM microresonator biosensor possesses such desirable merits as ease of operation, fast response, label free method, and high specificity, making it a promising candidate for in-situ DNA detection and related biosensing applications. [ABSTRACT FROM AUTHOR]