Time-Resolved and Temperature Tuneable Measurements of Fluorescent Intensity using a Smartphone Fluorimeter

A smartphone fluorimeter capable of time-based fluorescence intensity measurements at various temperatures is reported. Excitation is provided by an integrated UV LED (370 nm) and detection obtained using the in-built CMOS camera. A Peltier is integrated to allow measurements of the intensity over T = 10 to 40 C with a maximum temperature resolution of DELTA T ~ 0.1 C. All components are controlled using a smartphone battery powered Arduino microcontroller and a customised Android application that allows sequential fluorescence imaging and quantification every DELTA t = 4 seconds. The temperature dependence of fluorescence intensity for four emitters (Rhodamine B, Rhodamine 6G, 5,10,15,20-tetraphenylporphyrin and 6-(1,4,8,11-tetraazacyclotetradecane)2-ethyl-naphthalimide) are characterised. The normalised fluorescence intensity over time of the latter chemosensor dye complex in the presence of Zn ion is observed to accelerate with an increasing rate constant, k = 1.94 min-1 at T = 15 C and k = 3.64 min-1 at T = 30 C, approaching a factor of ~ 2 with only a change in temperature of DELTA T = 15 C. Thermally tuning these twist and bend associated rates to optimise sensor approaches and device applications is proposed.