2. Smartphone Intensity Fluorimeter

A smartphone intensity fluorimeter has been developed by combining the attributes of a smartphone’s in-built flash LED as an optical source and the CMOS camera as detector. By using the white LED, the instrument not only avoids the requirements of an external source and necessary power supply but also overcomes the issues associated with low irradiance and large mechanical hardware in using other in-built sources such as display AMOLED. Furthermore, the broad spectrum of the white LED can be filtered selectively in order to select any suitable excitation band for different application specific fluorescence sensors. For instance, the blue filtered emission (λ ~ 450 nm) has been utilized to excite a pH-responsive 4-aminonaphthalimide fluorophore (Hossain et al., Proc. SPIE 9634, 24th Optical Fiber Sensors Conferences, 2015), which fluoresces in the green region in the visible spectrum. The pH-responsive green fluorescence at λ ~ 530 nm is readily detected using the smartphone camera and a customised RGB app. Beyond monitoring the water quality at any specific location, the smartphone intensity fluorimeter also demonstrates the capability of generating a real-time pH map by collecting data from multiple points with the GPS coordinates of the corresponding locations.