Functionalized Gold Nanoparticles for the Detection of C-Reactive Protein

Abstract

C-reactive protein (CRP) is a very important biomarker of infection and inflammation for a number of diseases. Routine CRP measurements with high sensitivity and reliability are highly relevant to the assessment of states of inflammation and the efficacy of treatment intervention, and require the development of very sensitive, selective, fast, robust and reproducible assays. Gold nanoparticles (Au NPs) are distinguished for their unique electrical and optical properties and the ability to conjugate with biomolecules. Au NP-based probes have attracted considerable attention in the last decade in the analysis of biological samples due to their simplicity, high sensitivity and selectivity. Thus, this article aims to be a critical and constructive analysis of the literature of the last three years regarding the advances made in the development of bioanalytical assays based on gold nanoparticles for the in vitro detection and quantification of C-reactive protein from biological samples. Current methods for Au NP synthesis and the strategies for surface modification aiming at selectivity towards CRP are highlighted.

Numerical Modelling of the Optical Properties of Plasmonic and Latex Nanoparticles to Improve the Detection Limit of Immuno-Turbidimetric Assays

“…While Au NPs are the standard nanomaterials for optical or colorimetric sensing due to their long-term chemical stability [ 15 , 17 , 18 ], Ag NPs are renowned for the best plasmonic performance in the visible range [ 16 ]. For instance, the extinction cross-section of Ag NPs is 5–10 times larger than Au NPs with the same morphology, which may suggest a proportionally greater effect in hetero-aggregates [ 16 , 17 , 40 ].…”

“…Lowering the latex concentration is not a good strategy, because this is accompanied by the growth of the detection limit and the saturation of the available targeting units on the nanospheres with consequent saturation of the response, even if the total signal is within the spectrophotometric range of the turbidimeter (i.e., an optical absorption spectrometer working at a specific wavelength interval) [ 2 , 6 ]. Nonetheless, there is a continuous demand for lowering the detection limit to allow the use of small volumes of samples, such as in microfluidic circuits [ 7 , 15 ].…”

“…Au and Ag NPs have intense extinction bands in the visible range due to the collective excitation of conduction electrons (plasmons) [ 14 , 16 , 17 , 18 ]. These NPs have been widely exploited for spectrophotometric detection of analytes reaching a very low detection threshold also in homogeneous assays where the nanoparticles are mixed directly with the analyte in the liquid phase instead of being supported on a substrate [ 14 , 15 , 18 , 19 , 20 ]. Although in the subwavelength scale, advanced optical structures like self-assembled plasmonic nanoarrays and metamaterials provide significant sensitivity in biosensing assays, leading to the emergence of biosensors with an ultralow limit of detection at very low analyte concentrations [ 21 , 22 , 23 ], the homogeneous assays still have the advantage of low-cost and high-throughput in flow continuous analysis without the need for continuous replacement of the detection substrate for each sample [ 24 , 25 , 26 ].…”

“…The success of Au and Ag NPs in biosensing is connected to the large extinction (i.e., absorption plus scattering [ 16 , 17 ]) cross-section at the plasmon resonance band and to the rapid increase of optical density at longer wavelengths upon particles aggregation [ 14 , 15 ]. The appearance of plasmon resonance bands in the red and near-infrared is due to the electric dipole–dipole interaction and coupling between the plasmonic modes of neighbouring particles in the cluster [ 14 , 17 , 18 , 27 , 28 ].…”

Rapid Detection of Botulinum Neurotoxins—A Review

“…The tracking of colour change in relation to colloidal gold stems from the principle that certain wavelengths of light at the surface of the metal have the ability to excite the conduction electrons which in turn results in oscillation. It is this process that is referred to as localised surface plasmon resonance (LSPR) [111]. Gold colloids typically exhibit UV-visible spectra with distinctive absorption peak ranges of ~515–535 nm with respective nanoparticle diameters of 5–50 nm; this is due to their absorption of specific wavelengths of light due to LSPR [112].…”