Point‐of‐care (PoC) devices are being continuously developed because they can perform medical analyses quickly and at a reduced cost while being used out‐of‐lab without needing a professional analyst or technician. Additionally, due to their high sensitivity and selectivity, they aim to accurately diagnose diseases, even at an early stage. Smartphones are often chosen as the readout instrument for PoC devices due to their widespread availability, cost‐efficiency, computing power, compactness, and the numerous sensors they incorporate, including high‐performance cameras. Smartphone-based PoC devices frequently utilize fluorescence biosensors, commonly used in medical diagnostics due to their low detection limits. Although these biosensors can capture a single molecule, detecting its fluorescence, which would be the ultimate sensitivity of PoCs, is a significant challenge for a smartphone camera‐based device. For instance, the minimum detectable intensity demonstrated on a smartphone‐based microscope corresponds to the intensity of ten fluorescent molecules and requires a monochrome camera and an optical bench. To address this challenge, various complex amplification techniques are used to detect single molecules. For instance, multiple thermocycling processes can increase the number of analytes, or signal intensity can be boosted using optical nanoantennas. The first approach requires precise temperature control and careful timing for exchanging different reagents in the sample. The second approach involves a precise multi‐step protocol for preparing the biosensor, exhibiting intrinsic dispersion in their signal amplification, which can hinder accurate quantitative detection.
In this manner, this thesis aims to design a low‐cost, smartphone‐based fluorescence microscope that can detect a single fluorescent molecule without amplification techniques for either the signal or the number of analytes. This innovative microscope, capable of direct single fluorescence molecule detection, would enable various applications, including super‐resolution imaging.