Integrated fluorescence detection of labeled biomolecules using a prism-like PDMS microfluidic chip and lateral light excitation

Abstract

Microfabricated amorphous silicon photodiodes were integrated with prism-like PDMS microfluidics for the detection and quantification of fluorescence signals. The PDMS device was fabricated with optical quality surfaces and beveled sides. A 405 nm laser beam perpendicular to the lateral sides of the microfluidic device excites the fluorophores in the microchannel at an angle of 70° to the normal to the microchannel/photodiode surface. This configuration, which makes use of the total internal reflection of the excitation beam and the isotropy of the fluorescence emission, minimizes the intensity of excitation light that reaches the integrated photodetector. A difference of two orders of magnitude was achieved in the reduction of the detection noise level as compared with a normally incident excitation configuration. A limit-of-detection of 5.6 × 10(10) antibodies per square centimeter was achieved using antibodies labeled with a model organic fluorophore. Furthermore, the results using the lateral excitation scheme are in good proportionality agreement with those by fluorescence quantification using wide-field fluorescence microscopy.

Microfluidic ELISA for sensing of prostate cancer biomarkers using integrated a-Si:H p-i-n photodiodes

“…Our current work focuses on attempts to answer the optimization protocols/strategies for detection of tPSA at clinical limits, both from an immunological as well as a microfluidic perspective. Specific plans include use of integrated fluorescence filter-based photodiode for detection of quantum dots labeled anti-PSA antibodies (to enhance amplification) and on a longer perspective, exploit the lateral excitation mode [12] during photodiode detection (for avoidance of bleaching, to reduce scattering as well as to decrease the noise level). In conclusion, microfluidic platforms with integrated detection cam potentially open paths to addressing issues related to highthroughput multiplexing technologies to differentiate PCa patients from healthy controls effectively and with minimal ambiguity.…”

Miniaturization of fluorescence sensing in optofluidic devices

“…The materials usually used as substrates for the fabrication of PCBs are resistant at high temperatures (> 170 °C), this characteristic making them compatible with microfabrication techniques that involves elevated temperatures. The reliability and potential of PCBs for miniaturization of fluorescence sensing systems was demonstrated recently (Novo et al 2014;Shin et al 2015Shin et al , 2017Babikian et al 2017;Obahiagbon et al 2018). A PCB offers an integration alternative to glass/polymeric microfluidic chips, which are not integration-friendly with standard, off-the-shelf optoelectronic elements (Babikian et al 2017).…”

“…The phenomenon can be used to mitigate direct illumination of the detector and, by consequence, to lower the noise level. For example, a design solution using a lateral excitation configuration, to (1) maximize the photon flux exciting the microfluidic channel while (2) preventing excitation light reaching the sensor, was proposed by Novo et al (2014). This configuration (see Fig.…”

“…Two possible ways of liquid jet excitation: (1) orthogonal fluorescence excitation, and (2) optical fiber for Raman excitation. (a) Reproduced from (Novo et al 2014), Copyright 2014, with permission from The Royal Society of Chemistry. (b) Reproduced from (Persichetti et al 2017), Copyright 2017, with permission from The Royal Society of Chemistry efficient distribution to the photon detector, located on the opposite side of the fluidic chamber, while the light source (465 nm LED) and the photon detector were externally located.…”

A multidirectional beam steering reflector actuated by hydraulic control

“…Liquid prism-like devices controlled by hydraulic and pneumatic control have formed one of the significant branches in the area of optofluidics. These liquid prisms are usually fabricated by polydimethylsiloxane (PDMS) with or without liquid filling in the hollow prism 21 , 22 . These prisms can be highly integrated in the microchips, but the rigid geometry provides a limitation in developing the optofluidic systems.…”