Development of filterless, miniaturized fluorescence detection system

This work presents the fluorescence detection limits with commercially available detectors and development of miniaturized fluorescence detector. At the first part presents a method to enhance the fluorescence detection through a miniature cylindrical micro lens that is integrated into an engineered PDMS cuvette with high refractive index TiO2 impeded in. LED transmitter and blue laser diode, 450 nm were used as the excitation light sources and fluorescence detection systems were set at 90-degree without any filters. Square shape detected more fluorescence than circular shaped cuvette. Three different fluorophore holders were used in this work to investigate the micro lens focusing efficiency and TiO2 light reflection efficiency. Focusing efficiency of the lens and reflection efficiency of TiO2 were ranged 137-149% and 143-154 % respectively. The results showed that square cuvette resulted in a minimum detection limit of 30 nM, micro lens and micro lens together with TiO2 inclusion to the cuvettes recorded minimum detection limit as 20 nM and 10 nM respectively. Fluorescein was selected as fluorophore as it has higher quantum yield, and the sample volume was kept as 1 µl in all the experiments. Optical spectrometer used as detector in this part. Si PIN photodiode was used to detect the fluorescence in 1 µl volume. The fluorescein signal was amplified by op-amp receiver circuit. Blue laser was used as the light source at 450 nm of wavelength. Two receiver circuits were developed in order to enhance the fluorescence signal. 10 µM and 50 nM were the minimum detection limit of the photodiode with the receiver circuits. For the development of narrowband photodetector for detection of fluorescence, CsPbBr3 selected as perovskite material as it has excellent photophysical properties. However, poor stability of CsPbBr3 limited their applications in research field. The core shell structure has ability to enhance the stability of the CsPbBr3 QDs while reducing the surface defects of QDs. CsPbBr3 QDs were coated by thin layer of TiO2. 450 0C of temperature was selected as calcination temperature as it gave improved XRD spectrum. CsPbBr3 QDs/TiO2 core shell material-based photodetector was fabricated. The material was drop casted on to the Au electrode and measure the current by digital multimeter. The responsivity and stability of the material was good. Several issues in QDs layer-based devices should be addressed to improve the performance of the photodetector.