Abstract
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.
Highlights
Development of plasmonic biosensors combining reliability and ease of use is still a challenge
We describe an ultrasensitive and costeffective plasmon-enhanced fluorescence (PEF)-based immunosensor—consisting of 2D AuNP array functionalized by photochemical immobilization technique (PIT)—able to detect proteins at femtomolar level in whole human blood
The gold standard for diagnosing malaria relies on the microscopic examination of blood films that necessitates trained personnel, but is unsuitable for a rapid diagnosis, which is required for a favorable prognosis of the disease[62]
Summary
Development of plasmonic biosensors combining reliability and ease of use is still a challenge. Plasmonic nanostructures are realistic candidates to extend the limit of fluorescence detection to the femtomolar level and beyond[11,12] These devices modify the spectral properties of the nearby fluorescent dyes and do not necessitate expensive equipment, specific or toxic reagents, or significant modifications to well-established fluorescence-based assays. Such a modification depends strongly both on the spectral overlap between the fluorescent dye and the plasmon absorbance[13,14] and on the fluorophore-nanostructure distance z15–17. Such a collective effect is negligible if R < 2/3, in which case the plasmonic response of the 2Dlattice is well-described by a system of decoupled LSPs34
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