Development of plasmonic biosensors combining reliability and ease of use is still a challenge. Gold nanoparticle arrays made by block copolymer micelle nanolithography (BCMN) stand out for their scalability, cost-effectiveness and tunable plasmonic properties, making them ideal substrates for fluorescence enhancement. Here, we describe a plasmon-enhanced fluorescence immunosensor for the specific and ultrasensitive detection of Plasmodium falciparum lactate dehydrogenase (PfLDH)—a malaria marker—in whole blood. Analyte recognition is realized by oriented antibodies immobilized in a close-packed configuration via the photochemical immobilization technique (PIT), with a top bioreceptor of nucleic acid aptamers recognizing a different surface of PfLDH in a sandwich conformation. The combination of BCMN and PIT enabled maximum control over the nanoparticle size and lattice constant as well as the distance of the fluorophore from the sensing surface. The device achieved a limit of detection smaller than 1 pg/mL (<30 fM) with very high specificity without any sample pretreatment. This limit of detection is several orders of magnitude lower than that found in malaria rapid diagnostic tests or even commercial ELISA kits. Thanks to its overall dimensions, ease of use and high-throughput analysis, the device can be used as a substrate in automated multi-well plate readers and improve the efficiency of conventional fluorescence immunoassays.
Microelectrode arrays are widely used
in different fields such as neurobiology or biomedicine to read out
electrical signals from cells or biomolecules. One way to improve
microelectrode applications is the development of novel electrode
materials with enhanced or additional functionality. In this study,
we fabricated macroelectrodes and microelectrode arrays containing
gold penetrated by nanohole arrays as a conductive layer. We used
this holey gold to optically excite surface plasmon polaritons, which
lead to a strong increase in transparency, an effect that is further
enhanced by the plasmon’s interaction with cell culture medium.
By varying the nanohole diameter in finite-difference time domain
simulations, we demonstrate that the transmission can be increased
to above 70% with its peak at a wavelength depending on the holey
gold’s lattice constant. Further, we demonstrate that the novel
transparent microelectrode arrays are as suitable for recording cellular
electrical activity as standard devices. Moreover, we prove using
spectral measurements and finite-difference time domain simulations
that plasmonically induced transmission peaks of holey gold red-shift
upon sensing medium or cells in close vicinity (<30 nm) to the
substrate. Thus, we establish plasmonic and transparent holey gold
as a tunable material suitable for cellular electrical recordings
and biosensing applications.
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