Abstract
AbstractThe steadily increasing demand for accurate analysis of vitamin D level,viameasurement of its best general marker, 25-hydroxyvitamin D (25(OH)D), pushes for the development of novel automated assays capable of working at very low concentrations. Here, we propose a plasmonic biosensor of 25(OH)D3 (calcifediol) based on surface-enhanced infrared absorption spectroscopy, which exploits the resonant coupling between plasmonic nanoantennas and vibrational excitation of small molecules. Specifically, our proposed platform features a large-area (several mm2) metasurface made of gold nanoantennas fabricated on a silicon substrate, comprising different macroregions (“pixels”) of area 500 × 500 µm2. In each pixel, the nanoantenna geometrical parameters are tuned so as to support localized surface plasmon resonances (and hence large field enhancements at the nanoscale) within different regions of the infrared spectrum. As a result, a single chip is capable of performing analysis from the region of functional groups to that of fingerprint. Two different designs are fabricatedviaelectron beam lithography, functionalized with a correlated antibody for the detection of 25(OH)D3, and characterizedviaFourier-transform infrared spectroscopy. Our experiments demonstrate the capability to detect a concentration as low as 86 pmol/L, and an amount of immobilized small molecules of 25(OH)D3 monohydrate (molecular weight: 418.65 g/mol) as low as 4.31 amol over an area of 100 × 100 µm2.
Highlights
Given the continuous aging of the population, an increasing demand for analysis of 25-hydroxyvitamin D (25(OH)D), the best general indicator of vitamin D status, has been observed worldwide since the early 2000s [1]
We report on the experimental detection of 25(OH)D3 by exploiting plasmonic metasurfaces based on 2-D arrays of gold NAs on a silicon substrate
The mild disagreement between experimental and simulated responses is attributable to the slight deviations between the geometrical parameters of the manufactured nanostructures and the nominal ones, which are due to the electron beam lithography (EBL) manufacturing procedure [35]
Summary
Given the continuous aging of the population, an increasing demand for analysis of 25-hydroxyvitamin D (25(OH)D), the best general indicator of vitamin D status, has been observed worldwide since the early 2000s [1]. The deficiency of vitamin D in elderlies is often associated with cognitive decline (PMID: 23185713), bone diseases (PMID: 31792684), impaired muscle strength, and reduced physical performance (PMID: 31686797). Such deficiency has been associated with other medical conditions, including diabetes, cancer, autoimmune and cardiovascular diseases, all of which can increase mortality. Vitamin D is a challenging analyte to measure accurately, because of its highly lipophilic nature, high affinity for binding proteins, as well as the presence of multiple vitamin D metabolites in the circulation. A recent study [2] on newly introduced automated assays for the measurement of 25(OH)D found that they generally perform satisfactorily at high concentrations (258 nmol/L), but tend to fail at low concentrations; 50% and 100% of the examined assays
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