Label-Free Biochemical Sensing Using Processed Optical Fiber Interferometry: A Review

Post-Selection Design of Aptamers: Comparative Study of Affinity of the DNA Aptamers to Recombinant Extracellular Domain of Human Epidermal Growth Factor Receptors

The current work presents comparative assessment of affinity of the designed DNA aptamers for extracellular domain of the human epidermal growth factor receptor (EGFR*). The affinity data of the 20 previously published aptamers are summarized. Diversity of the aptamer selection methods and techniques requires unification of the comparison algorithms, which is also necessary for designing aptamers used in the post-selection fitting to the target EGFR* protein. In this study affinities of the DNA aptamers from two families, U31 and U2, previously obtained by Wu et al. from the same selection [Wu et al. (2014) PLoS One, 9, e90752] and their derivatives - GR20, U2s, and Gol1 obtained by us through rational design, were compared. Affinity of the aptamers to EGFR* was measured by two different methods: a solution-phase technique - fluorescence polarization of FAM-labeled aptamers, and by a kinetic method using biolayer interferometry technique with aptamers immobilized on the surface. Unlike the values of equilibrium dissociation constants obtained through titration and expressed in units of protein concentration, analysis of the titration curve profiles themselves and kinetics of interaction proved to be more informative. This allowed us to identify how even subtle changes in the aptamers and their structures affect affinity. Hypotheses regarding the "structure-function" relationships and recognition mechanisms were formulated. The data obtained for the set of aptamer constructs are critical for moving forward to examination of aptamer interactions with EGFR on the cell surface.

Optical fiber sensing probe for detecting a carcinoembryonic antigen using a composite sensitive film of PAN nanofiber membrane and gold nanomembrane

An optical fiber sensing probe using a composite sensitive film of polyacrylonitrile (PAN) nanofiber membrane and gold nanomembrane is presented for the detection of a carcinoembryonic antigen (CEA), a biomarker associated with colorectal cancer and other diseases. The probe is based on a tilted fiber Bragg grating (TFBG) with a surface plasmon resonance (SPR) gold nanomembrane and a functionalized polyacrylonitrile (PAN) PAN nanofiber coating that selectively binds to CEA molecules. The performance of the probe is evaluated by measuring the spectral shift of the TFBG resonances as a function of CEA concentration in buffer. The probe exhibits a sensitivity of 0.46 dB/(µg/ml), a low limit of detection of 505.4 ng/mL in buffer, and a good selectivity and reproducibility. The proposed probe offers a simple, cost-effective, and a novel method for CEA detection that can be potentially applied for clinical diagnosis and monitoring of CEA-related diseases.

Precise detection of trace level protein using MIP-MoS2 nanocomposite functionalized PCF based interferometer

Fiber optic interferometry combined with recognizing elements has attracted intensive attention for the development of different biosensors due to its superior characteristic features. However, the immobilization of sensing elements alone is not capable of low-concentration detection due to weak interaction with the evanescent field of the sensing transducer. The utilization of different 2D materials with high absorption potential and specific surface area can enhance the intensity of the evanescent field and hence the sensitivity of the sensor. Here, a biosensor has been fabricated using an inline hetero fiber structure of photonic crystal fiber (PCF) and single-mode fiber (SMF) functionalized with a nanocomposite of molybodenum di-sulfide (MoS2) and molecular imprinting polymer (MIP) to detect trace levels of bovine serum albumin (BSA). The sensor showed a wide dynamic detection range with a high sensitivity of 2.34 × 107 pm/µg L-1. It shows working potential over a wide pH range with a subfemtomolar detection limit. The compact size, easy fabrication, stable structure, long detection range, and high sensitivity of this sensor would open a new path for the development of different biosensors for online and remote sensing applications.