Robust Smartphone Assisted Biosensing Based on Asymmetric Nanofluidic Grating Interferometry

Abstract

Point-of-care systems enable fast therapy decisions on site without the need of any healthcare infrastructure. In addition to the sensitive detection, stable measurement by inexperienced persons outside of laboratory facilities is indispensable. A particular challenge in field applications is to reduce interference from environmental factors, such as temperature, to acceptable levels without sacrificing simplicity. Here, we present a smartphone-based point-of-care sensor. The method uses an optofluidic grating composed of alternating detection and reference channels arranged as a reflective phase grating. Biomolecules adsorbing to the detection channel alter the optical path length, while the parallel reference channels enable a direct common mode rejection within a single measurement. The optical setup is integrated in a compact design of a mobile readout device and the usability is ensured by a smartphone application. Our results show that different ambient temperatures do not have any influence on the signal. In a proof-of concept experiment we measured the accumulation of specific molecules in functionalized detection channels in real-time and without the need of any labeling. Therefore, the channel walls have been modified with biotin as capture molecules and the specific binding of streptavidin was detected. A mobile, reliable and robust point-of-care device has been realized by combining an inherently differential measurement concept with a smartphone-based, mobile readout device.

Nanofluidic Immobilization and Growth Detection of Escherichia coli in a Chip for Antibiotic Susceptibility Testing

“…With an improved measurement setup, the presented detection principle could prove useful in future point-of-care devices for antimicrobial susceptibility testing (AST) where no overnight culture and labeling of the bacteria is possible. It has been shown that a similar optical setup can be realized for protein detection based on a smartphone [ 25 ]. In future studies, we plan to investigate if a dependence of the antibiotic concentration can be correlated with the measuring signal of the setup.…”

“…Therefore, a hydrodynamic bacterial cell-trapping principle which has been recently been reported [ 24 ] is now implemented in the form of a regular nanogap array to allow readout with an interferometric method. Here, we present an optofluidic chip which can immobilize bacteria in an optical asymmetric grating to measure the proliferation of bacteria with high sensitivity by interferometry based on optofluidic concepts that, in the past, had been developed to measure surface bound molecules [ 25 , 26 ]. This study describes the fabrication and characterization of the optofluidic nanosystem and shows the applicability of this approach in future ASTs.…”

Advances in Label-Free Detections for Nanofluidic Analytical Devices

“…Purr et al prepared a device with asymmetric interdigitating arrangement of detection and reference nanochannels to directly calculate the refractive index [ 23 ]. This nanofluidic device could also be integrated into a smartphone-based biosensing system [ 24 ].…”