Resolution-improved in situ DNA hybridization detection based on microwave photonic interrogation

Fiber-integrated WGM optofluidic chip enhanced by microwave photonic analyzer for cardiac biomarker detection with ultra-high resolution

Cardiac troponin I (cTnI) plays an important role in emergency diagnosis of cardiovascular diseases, which exists predominately in the form of cardiac troponin I-C (cTnI-C) complex. We proposed a fiber-integrated optofluidic chip immunosensor with time-delay-dispersion based microwave photonic analyzer (MPA) for cTnI-C detection. The whispering gallery mode (WGM) fiber probe was fabricated by embedding a polydopamine functionalized hollow glass microsphere (HGMS) into the etched capillary-fiber structure, and the WGMs could be excited through the efficient coupling between the thin-wall capillary and the HGMS. The reflective WGM optofluidic chip functioned as a wavelength tuner to construct fiber ring laser cavity, whose laser output wavelength was cTnI-C concentration-dependent. The tiny wavelength variation of sensing laser was converted into a radio-frequency (RF) response, which was retrieved by measuring the change of RF-domain free spectrum range (FSR) in time-delay-dispersion based MPA, and the quantitative detection of cTnI-C complex can be achieved with high resolution. Experimental results show that this immunosensor had a limit of detection (LOD) of 0.59 ng/mL, and a detection resolution of 1.2 fg/mL. The relative resolving power was 10²-10⁴-fold higher than that of others optical fiber cTnI biosensors. The proposed fiber-integrated optofluidic chip provides an innovative lab-on-chip diagnostic tool for myocardial damage.

High-speed refractive index sensing system based on Fourier domain mode locked laser

A high-speed refractive index sensing system based on the Fourier domain mode locked laser (FDML) and a microfiber Bragg grating (mFBG) is theoretically studied and experimentally demonstrated. Unlike traditional physical parameter sensing systems, which directly use the FDML as the wavelength scanning source and the optical sensor as the spectra shaping component, we inserted an mFBG into the FDML cavity in order to generate time domain pulse signals used for sensing. The wavelength shift in optical frequency domain is converted into time domain pulse drift. The sensitivity of the proposed refractive index (RI) sensing system is improved by two orders of magnitude, compared with the wavelength monitoring method. The scanning speed is as high as 43 kHz. Moreover, the sensitivity curve can be adjusted by tuning the direct current voltage. The nonlinear sensitivity and linear sensitivity with RI can be achieved.

Experimental and theoretical investigation for surface plasmon resonance biosensor based on graphene/Au film/D-POF

A D-shape plastic optical fiber (D-POF) surface plasmon resonance (SPR) biosensor based on the graphene/Au film (G/Au) was proposed and experimentally demonstrated for detection of DNA hybridization process. To improve the detection performance of SPR sensors, the Physical Vapor Deposition (PVD) method was used to evaporate the Au film directly onto the graphene grown on copper foil, and the Au film acted as a role of traditional Polymethyl Methacrylate (PMMA). The process made graphene and Au film form seamless contact. Next, the G/Au was transferred onto the D-shape fiber together. We explored the G/Au SPR sensor by using the finite element method (FEM) and obtained the optimum materials thickness to form configuration. Compared to other plastic optical fiber experiments, the proposed sensor's sensitivity was improved effectively and calculated as 1227 nm/RIU in a range of glucose solution. Meanwhile, our proposed sensor successfully distinguishes hybridization and single nucleotide polymorphisms (SNP) by observing the resonance wavelength change. It also exhibits a satisfactory linear response (R² = 0.996) to the target DNA liquids with respective concentrations of 0.1nM to1µM, which shows this method's wide potential in medical diagnostics.