A composite optical filter greenly fabricated for living algae detection.

The integration of optical filtration functionality into a lens and a microfluidic chip represents a promising approach for reducing the size of a microfluidic device. Greenly fabricating a composite polydimethylsiloxane (PDMS) filter (C-filter) with optical amplification function for chlorophyll fluorescence detection was proposed in this work. The core idea is to make the PDMS microfluidic chip as one sub-filter (S-filter) and enable another sub-filter amplification function (F-lens). The S-filter was prepared by soaking a PDMS microfluidic chip into Sudan II dye solved with ethanol. The F-lens is manufactured by sequentially mixing ethanol-solved crystal violet and the dimethyl-methylhydrogenosiloxane and dimethyl-methylvinylsiloxane for lens molding. Experimental results show that ethanol can serve as an effective and green substitute for phenol and toluene for dye dissolving. The dimethyl-methylhydrogenosiloxane can well dissolve crystal violet. The S-filter can filter light within the wavelength range of 400-500 nm, while the F-lens can filter light in the wavelength range of 500-650 nm. The C-filter shows a transmittance of 99.33 % in the wave length range of 650-710 nm, which is superior to the 96.72 % transmittance of commercial filters and is well-suited for living algae detection.