Optical manipulation of phototactic microalgae

Abstract

Light is essential for life to thrive and species have varied reactions to its presence. In this paper we investigate the phototactic properties of Chlorococcus sp., native in Idyang Umiray, Quezon province (15°12'2" longitude East, 121°25'2" latitude North). This species belongs to the Phylum Cyanophyta, more commonly known as blue-green algae because its chromophores are chlorophyll a and b. Algae are the primary producers of food in their ecosystem and therefore play a vital role in maintaining the stability of the food chain.
There is extensive research being done on photobiology, the study of the reactions of various life forms to light. Special concern is placed on the photoreceptors and circadian synchrony because it affects the organisms' behavior.
It has been long known that chlorophyll a has a broad absorption spectrum in the red and the blue band of the visible light spectrum, exploiting this could provide a more efficient means of manipulating microorganisms by optical means instead of the usual manual approach which is slow and tedious.
We investigate the phototaxis phenomenon by examining how the algae react to the presence of microsized optical gratings that are formed by the interference pattern produced by a triangular common-path interferometer (TCP) with a 35 mW He-Ne laser source (λ = 632.8 nm).