Several organisms possess 'ion channels' (gateways that selectively allow charged particles called ions to enter the cells and are integral for cell function) called channelrhodopsins, that can be switched on and off with the help of light. Different channelrhodopsins respond to different wavelengths in the light spectrum. These channels can be expressed in foreign organisms (animals and humans) by means of genetic engineering, which in turn finds applications in optogenetics, or the application of light to modulate cellular and gene functions. Until now, the shortest wavelength that a channelrhodopsin responds to was blue.