Optical sensors are demonstrating the largest potential for Lab-on-a-chip (LOC) systems to perform sensitive, quantitative, and fast sensing for healthcare and environmental monitoring. Among all options, biosensors based on refractometric sensing schemes combine high sensitivity with label-free detection, however, most of them still have not yet been miniaturized in LOC devices for the analysis of biological targets. Here, we demonstrate for the first time a fully miniaturized optical biosensor based on plasmonic-sensing that enables quantitative detection of biological analytes that are potentially found in milk (lactoferrin, streptomycin). The sensor relies on the unprecedented combination of i) miniaturized, monolithically integrated, and cost-effective optical transduction elements such as organic light-emitting diodes and organic photodiodes, and ii) immunoassay-based bio-recognition elements, for highly sensitive and specific localized surface plasmon resonance (LSPR) based detection via a nanostructured plasmonic grating. The sensor is also equipped with portable read-out electronics and microfluidic circuitry, allowing fast, reproducible and reliable functioning. The quantitative response is calibrated through reference samples and it allows reaching a limit of detection of 10-4 refractive index units (RIU) as LSPR sensor. The quantitative and analyte-specific detection is demonstrated for lactoferrin in the laboratory, giving a sensitivity as low as 9 ug/mL. The presented work opens the way for the universal application of optical biosensors in LOC devices, for on-site food analysis, and health monitoring, among others.
This work received funding from the European Union's Horizon 2020 research and
innovation programme under grant agreement no. 780839 (MOLOKO) and no. 101016706 (h-ALO).
The integration of multiple devices in a single functional unit is boosting the advent of a series of compact optical sensors for rapid and on-site analysis. In this context, the huge potential of plasmonic-based sensors has been affected by the strict constraints of the detection scheme. The need for laboratory equipment, such as laser sources and expensive prism-based optics, results therefore in not-portable systems.
Here, an ultra-compact plasmonic sensor is demonstrated through the smart-integration of an organic light-emitting transistor (OLET), an organic photodiode (OPD), and a nanostructured plasmonic grating (NPG).[1] The direct integration of the OPD onto the planar structure of the OLET provided an unprecedented high degree of proximity of the light-source and light detecting areas, which enabled the exploitation of the angle-dependent sensing characteristics of the NPG.
The most effective 3D layout of integration, including the optimal size and relative positioning of the three elements (i.e. OLET, OPD, and NPG), was unravelled by an advanced simulation tool, which also predicted the signal variation of the sensor under different conditions. Accordingly, the effectiveness of the new plasmonic-based detection scheme was demonstrated by the dependence of the OPD photocurrent on the surrounding environment of the NPG. In particular, a variation of the OPD photocurrent of about 10-9 A was recorded when exposing the NPG from water to alcoholic solutions at different concentrations.
A miniaturized plasmonic sensor with a total size of 0.1 cm3 was therefore obtained through the smart integration of nanometer-thick optoelectronic and plasmonic components.
[1] M. Prosa, et. al. Adv. Funct. Mater. 2021, 2104927. https://doi.org/10.1002/adfm.202104927
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