On-site analysis of multiple analytes from different classes (such as heavy metals, proteins and small molecules), at the sensitivity required for a selected application, is a hard technological challenge. In this context, optical sensing in miniaturized systems has the largest potential. Baser on our previous findings,[1-3] we present here the design and optimization of a miniaturized optical sensor with multiple channels, capable of multimodal optical detection in each channel, and the proof-of-concept realization of sub-systems providing two complementary detection modes: plasmon enhanced fluorescence and localized surface plasmon resonance. The multichannel (enabling multiplexing) and multimodal optical sensor is designed to have a total size of one inch-square and optimized sensing performance, obtained by combining organic optoelectronic and nanoplasmonic components.
[12] M. Prosa et al., Adv. Funct. Mater. 31 (2021).
[13] M. Bolognesi et al., Adv. Mater. 2208719 (2023) 1–13.
[14] F. Floris et al., Mater. Proc. 14 (2023) 1–5.
Within light sensing optoelectronic devices, multijunction organic and hybrid photodetectors show a large potential. In particular, organic and hybrid phototransistors hold promises for high-sensitivity thanks to their inherent signal-amplification characteristics. However, often a trade-off between a large sensing area, a fast response, and a high specific detectivity is difficult to be achieved. Here we propose an alternative phototransistor concept, that relies on a geometrically engineered large area tri-channel architecture, applied to a multilayer hybrid phototransistor composed of an inorganic In2O3/ZnO n-type field-effect channel, and a top organic bulk-heterojunction or hybrid perovskite light-sensing layer. Up-scalable solution-processing of both the field-effect channel and the light-sensing layers are implemented. Different photoactive layers are used to corroborate and validate the proposed concept. The resulting phototransistor combines the characteristics of easy solution processing, a maximum responsivity of 10^5 A/W thanks to the large electron mobility of the In2O3/ZnO heterointerface, and a maximum specific detectivity of 10^15Jones (at a low gate voltage of 5V and under a low light illumination of 10 nW/cm2), thanks to the large sensing area which is fully exploited in the tri-channel architecture. The improved photoresponse characteristics are accompanied by a fast response (risetime <10ms down to the uW/cm2 of illumination), which is comparable to the time-response of analogous phototransistors in the conventional architecture. The experimental data are supported by device modelling, which helps highlighting the peculiar advantages of the proposed large area, tri-channel and multi-junction phototransistor architecture.
Optical biosensors based on plasmonic sensing schemes combine high sensitivity and selectivity with label-free detection. However, the use of bulky optical components is still hampering the possibility of obtaining miniaturized systems required for analysis in real settings [1]. Here, we demonstrate a fully miniaturized optical biosensor prototype based on plasmonic detection that enables fast and multiplex sensing of analytes with high- and low-molecular weight (80000 and 582 Dalton) as quality and safety parameters for milk: a protein (lactoferrin) and an antibiotic (streptomycin). The optical sensor is based on the smart integration of (i) miniaturized organic optoelectronic devices used as light-emitting and -sensing elements and (ii) a functionalized nanostructured plasmonic grating for highly sensitive and specific localized surface plasmon resonance (SPR) detection [2]. The sensor provides quantitative and linear response reaching a limit of detection of 10^-4 refractive index units once it is calibrated by standard solutions. Analyte-specific and rapid (15 minute-long) immunoassay-based detection is demonstrated for both targets. By using a custom algorithm based on principal-component analysis, a linear dose-response curve is constructed which correlated with a limit of detection (LOD) as low as 3.7 μg/mL for lactoferrin, thus assessing that the miniaturized optical biosensor well-aligned with the reference benchtop SPR method [3].
Despite fluorescent sensing is a reference method for the detection of a plethora of different compounds, the exploitation of this class of sensors is still limited to a few application scenarios as a result of the restricted availability of miniaturized, portable, and user-friendly devices.
Here, the smart combination of an organic photodiode (OPD), a Distributed Bragg Filter (DBR), and an organic light-emitting diode (OLED) is proven to provide a stacked device architecture capable of detecting fluorescent signals for a wide range of concentrations of “Rhodamine 700” ranging from 10-3 M to 10-6 M.
Despite fluorescent sensing is a reference method for the detection of a plethora of different compounds, the exploitation of this class of sensors is still limited to a few application scenarios as a result of the restricted availability of miniaturized, portable, and user-friendly devices.
Here, the smart combination of an organic photodiode (OPD), a Distributed Bragg Filter (DBR), and an organic light-emitting diode (OLED) is proven to provide a stacked device architecture capable of detecting fluorescent signals for a wide range of concentrations of “Rhodamine 700” ranging from 10-3 M to 10-5 M.
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
We report on the characteristics of a host-guest lasing system obtained by co-evaporation of an oligo(9,9-diarylfluorene)
derivative named T3 with the red-emitter
4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye
(DCM). We demonstrate that the ambipolar semiconductor T3 can be implemented as active matrix in the realization of a
host-guest system in which an efficient energy transfer takes place from T3 matrix to the lasing DCM molecules. We
performed a spectroscopic study on the system by systematically varying the DCM concentration in the T3 matrix.
Measurements of steady-state photoluminescence (PL), PL quantum yield (PLQY) and amplified spontaneous emission
(ASE) threshold are used to optimize the acceptor concentration at which the ASE from DCM molecules takes place
with the lowest threshold.
Organic light-emitting diodes (OLEDs) implementing the DCM:T3
host-guest system as recombination layer are
fabricated for verifying the optical properties of the optimised blend in real working devices.
Indeed, the very low ASE threshold of T3:DCM makes the investigated blend an appealing system for use as active layer
in lasing devices. In particular, the ambipolar charge transport properties of the T3 matrix and its field-effect
characteristics make the host-guest system presented here an ideal candidate for the realization of electrically-pumped
organic lasers.
Organic light emitting transistors (OLET) have been recently demonstrated as innovative architectures combining into an integrated optoelectronic device multi-functional properties namely, the driving ability of a transistor device with the conversion of electrical current into efficient light emission via electronic relaxation of organic semiconductors. State of the art materials, achievement and performances will be presented and discussed in view of possible OLET architectures exploitation as electrically pumped organic nanolasers.
The dynamics of triplet recombination in fluorene trimers have been studied using steady state photoinduced absorption
(PA) spectroscopy. We investigated two type of oligomeric films, deposited by different techniques: thermal evaporation
and spincoating. The different molecular arrangement in both films is manifested in a red-shift of the absorption, PL and
T1-Tn triplet PA spectra of the sublimated film relative to the spincoated one. Triplet recombination dynamics follow a
dispersive bimolecular recombination model away from the trap filling regime.
Moreover we report on the characteristics of a host-guest lasing system obtained by co-evaporation of the most
promising oligofluorene derivative (T3) with the red-emitter
4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (DCM). The blend satisfies the necessary condition for an efficient Förster energy transfer to take place
from T3 matrix to DCM molecules.
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