Self-tuning interfacial architecture for Estradiol detection by surface plasmon resonance biosensor

Phosphorescent palladium-tetrabenzoporphyrin indicators for immunosensing of small molecules with a novel optical device

Small-molecule detection is important for many applications including clinical diagnostics, drug discovery, environmental screening, and food technology. Current techniques suffer from various limitations including cost, complex sample processing, massive instrumentation, and need for expertise. To overcome these limitations, a new optical immunosensing assay for the detection of small molecules was developed and assessed with the targets estrone (E1) and estradiol (E2). For this purpose, phosphorescent indicators were designed based on the tetrabenzoporphyrin skeleton directly linked to E1 or E2, or attached through a linker, with phosphorescence lifetimes in the range of ~100-~300 μs. The assay is an indicator displacement assay (IDA). The best performances of our optical immunosensor were obtained with the indicators E1-L-Por and E2-L-Por. As they bound to specific polyclonal antibodies, their phosphorescence (τ ~200 μs) was quenched. When an endogenous competitor was added, the indicator was displaced, and the phosphorescence was immediately recovered. These effects were measured with a new optical device, described here, and able to detect picograms of luminescent molecules emitting in the NIR range, simply by measuring phosphorescence decay. This radical switch-off/switch on process demonstrates that E1-L-Por and E2-L-Por are good candidates for in vivo and in vitro immunosensing of E1 and E2. Importantly, the present immunosensing assay can be easily adapted to other small molecules such as other hormones and drugs.

Optical Biosensors for Label-Free Detection of Small Molecules

Label-free optical biosensors are an intriguing option for the analyses of many analytes, as they offer several advantages such as high sensitivity, direct and real-time measurement in addition to multiplexing capabilities. However, development of label-free optical biosensors for small molecules can be challenging as most of them are not naturally chromogenic or fluorescent, and in some cases, the sensor response is related to the size of the analyte. To overcome some of the limitations associated with the analysis of biologically, pharmacologically, or environmentally relevant compounds of low molecular weight, recent advances in the field have improved the detection of these analytes using outstanding methodology, instrumentation, recognition elements, or immobilization strategies. In this review, we aim to introduce some of the latest developments in the field of label-free optical biosensors with the focus on applications with novel innovations to overcome the challenges related to small molecule detection. Optical label-free methods with different transduction schemes, including evanescent wave and optical fiber sensors, surface plasmon resonance, surface-enhanced Raman spectroscopy, and interferometry, using various biorecognition elements, such as antibodies, aptamers, enzymes, and bioinspired molecularly imprinted polymers, are reviewed.