A Counter Propagating Lens‐Mirror System for Ultrahigh Throughput Single Droplet Detection

Abstract

Fluorescence‐based detection schemes provide for multiparameter analysis in a broad range of applications in the chemical and biological sciences. Toward the realization of fully portable analysis systems, microfluidic devices integrating diverse functional components have been implemented in a range of out‐of‐lab environments. That said, there still exits an unmet and recognized need for miniaturized, low‐cost, and sensitive optical detection systems, which provide not only for efficient molecular excitation, but also enhanced photon collection capabilities. To this end, an optofluidic platform that is adept at enhancing fluorescence light collection from microfluidic channels is presented. The central component of the detection module is a monolithic parabolic mirror located directly above the microfluidic channel, which acts to enhance the number of emitted photons reflected toward the detector. In addition, two‐photon polymerization is used to print a microscale‐lens below the microfluidic flow channel and directly opposite the mirror, to enhance the delivery of excitation radiation into the channel. Using such an approach, it is demonstrated that fluorescence signals can be enhanced by over two orders of magnitude, with component parallelization enabling the detection of pL‐volume droplets at rates up to 40 000 droplets per second.

Recent Development of Optofluidics for Imaging and Sensing Applications

“…For example, Holzner et al used thermal reflow to change the pillar array to a microlens array on a glass substrate [30]. Compared to UV lithography, two-photon stereolithography represents a powerful technique to fabricate structures with a resolution down to submicrometer level and has excellent capability to fabricate the mold with high-resolution 3D structures [7,28,[32][33][34]. For example, Tang et al employed two-photo stereolithography to fabricate a mold incorporated with a cascaded 3D microlens for sensitivity-adjustable refractive index (RI) sensing [33].…”

“…Dietvorst et al designed a microfluidic-controlled optical router in which the light was totally reflected at the air filled chamber wall [51]. Cao et al deposited a silver/gold layer as a micro-reflecting matrix on the surface of an integrated PDMS cavity to enhance the light collection efficiency [34].…”

“…Therefore, high throughput of cytometry up to 50,000 cells per second was demonstrated. In addition, Cao et al manufactured a lens-mirror optofluidic system for ultrahigh throughput single droplet detection [34], as shown in Figure 3c. In this system, a spherical cavity was integrated with a flow channel and coated with silver and gold layers as a bottom mirror.…”

The Rise of the OM-LoC: Opto-Microfluidic Enabled Lab-on-Chip

“…In addition, monolithic parabolic mirrors and printed lenses have recently been fabricated above/below microfluidic channels respectively [140] through 2-photon polymerisation. This both improves sensitivity and high-throughput multi-phase droplet detection through enhanced photon excitation and collection, as seen in Figure 23d.…”

A 3D-cascade-microlens optofluidic chip for refractometry with adjustable sensitivity

“…36 Cao et al used two-photon stereolithography to fabricate a lens-mirror system for high-throughput droplet detection. 37 In our previous work, 31,38 we fabricated two in-plane 3D microlenses using two-photon stereolithography to reduce the light loss for sensitive absorbance measurements. Therefore, two-photon stereolithography is an ideal technology to fabricate cascaded 3D in-plane microlenses.…”