Droplet-Based Optofluidic Switch as a Controllable Optical Pulse-Width Modulator

Optical-Switch-Enabled Microfluidics for Sensitive Multichannel Colorimetric Analysis

“…For example, Cao et al and Dietvorst et al developed microbubble-based and microfluid-based optical routers, achieving response times of 1.8 and 3.3 s, respectively. , Importantly, the short response time accessible in our system is suitable for multichannel absorbance measurements and the extraction of kinetic data with a time resolution on the second scale. It should be noted, although faster optical switching has been achieved using a TIR-based droplet approach, it is relatively difficult to control droplet position for the controllable multichannel applications. In contrast, by virtue of the use of pneumatic microvalves, each of the “light-transmitting” and “light-blocking” fluid entities in the current system can be independently manipulated and positioned, allowing programmable operation in multichannel formats.…”

“…The phenomenon of total internal reflection (TIR) can be used to abruptly change the direction of light through careful choice of the light incident angle and media refractive indices at a dielectric interface. Using this principle, optical switches have been realized within a range of microfluidic systems. − That said, for such reflection-based switches, due to the need to sensitively control the incident angle to realize TIR, complex structure layouts must be created for multichannel applications. In contrast, for light-absorption-based optical switches, fluidic layouts can be simplified because of the independence on the incident angle of light.…”

“…The dynamic manipulation of “light-transmitting” and “light-blocking” fluids using an appropriate pumping system is critical for the practical application of optical switches and characterized by tunable switching frequencies, operational automation, and reliability. Droplets can be continuously generated in a two-phase system using syringe pumps to modulate the light . Nevertheless, it is relatively difficult to manipulate and position individual droplets in a bespoke manner, thus limiting the user’s ability to precisely control multiple optical switches.…”

“…Droplets can be continuously generated in a two-phase system using syringe pumps to modulate the light. 19 Nevertheless, it is relatively difficult to manipulate and position individual droplets in a bespoke manner, thus limiting the user's ability to precisely control multiple optical switches. Alternatively, droplet manipulation can be achieved through the use of pneumatic microvalves which are powerful tools for controlling fluids in microfluidic channels.…”