Smartphone-based point-of-care (POC) technologies have emerged as ideal next-generation point-of-care devices (POCD) for in vitro diagnostics (IVD). For luminescent detection, the measurement is performed in the dark using a plano-convex lens in front of the smartphone camera for converging the field of view. Nowadays, various prospective smartphone-based POC luminescence detection devices have been developed that enable the determination of many analytes. The colorimetric content of color digital images can be numerically analyzed by retrieving pixel intensities. As such, the built-in camera of a smartphone can effectively capture color and structural information on Microfluidic devices, and the integration of a smartphone camera and a Microfluidic chip effectively reduces the complexity and cost of a POC technologies system.
Fig.1 The assembled smartphone-based device with luminescence detection. (Cevenini, 2016)
Various prospective smartphone-based POC luminescence detection devices have been developed, such as assay for total cholesterol or bile acid in serum; multiplexed homogeneous assays for the proteolytic: trypsin, chymotrypsin and enterokinase and toxicity assay.
The assay is performed in a disposable mini-cartridge. It employs low-cost 3D printing for the fabrication of a smartphone attachment and a compact mini-cartridge. The mini-cartridge comprises a blood separator pad holder with an LF1 glass fiber filter for the one-step serum separation from whole blood. The developed POC assays detect cholesterol and 3α-hydroxy bile acid in real sample matrices using only minute sample volume.
Fig.2 Schematic of the mini-cartridge. (Roda, 2014)
The applications of smartphone-based POC luminescence detection in whole-cell toxicity include lateral flow immunoassay and enzymatic assays for the detection of biomarkers in biological fluids and other bioanalytical applications. The biosensors can detect general toxicity or environmental pollutants including heavy metals, endocrine disruptors, explosives.
Antibody detection is important in many diagnostic and bioanalytical assays. A new sensor platform based on bioluminescence allows the detection of antibodies directly in a solution using a smartphone as the sole piece of equipment. The new sensor platform is single-protein sensors that consist of the blue-light emitting luciferase NanoLuc connected via a semiflexible linker to the green fluorescent acceptor protein mNeonGreen, which are kept close together using helper domains. The binding of an antibody to epitope sequences flanking the linker disrupts the interaction between the helper domains, resulting in a large decrease in Bioluminescence Resonance Energy Transfer efficiency. The resulting change in color of the emitted light from green-blue to blue can be detected directly in blood plasma, even at pM concentrations of antibody.
The key advantages of bioluminescence detection are that the optical signal is generated in situ and is thus detected against a dark background, and that it does not require substantial sample preparation or Microfluidic circuitry. A key contributor of luminescence detection is sensitivity, ease-of-use, small size and high stability.
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