Double-Resonant Nanostructured Gold Surface for Multiplexed Detection

Abstract

A novel double-resonant plasmonic substrate for fluorescence amplification in a chip-based apta-immunoassay is herein reported. The amplification mechanism relies on plasmon-enhanced fluorescence (PEF) effect. The substrate consists of an assembly of plasmon-coupled and plasmon-uncoupled gold nanoparticles (AuNPs) immobilized onto a glass slide. Plasmon-coupled AuNPs are hexagonally arranged along branch patterns whose resonance lies in the red band (∼675 nm). Plasmon-uncoupled AuNPs are sprinkled onto the substrate, and they exhibit a narrow resonance at 524 nm. Numerical simulations of the plasmonic response of the substrate through the finite-difference time-domain (FDTD) method reveal the presence of electromagnetic hot spots mainly confined in the interparticle junctions. In order to realize a PEF-based device for potential multiplexing applications, the plasmon resonances are coupled with the emission peak of 5-carboxyfluorescein (5-FAM) fluorophore and with the excitation/emission peaks of cyanine 5 (Cy5). The substrate is implemented in a malaria apta-immunoassay to detect Plasmodium falciparum lactate dehydrogenase (PfLDH) in human whole blood. Antibodies against Plasmodium biomarkers constitute the capture layer, whereas fluorescently labeled aptamers recognizing PfLDH are adopted as the top layer. The fluorescence emitted by 5-FAM and Cy5 fluorophores are linearly correlated (logarithm scale) to the PfLDH concentration over five decades. The limits of detection are 50 pM (1.6 ng/mL) with the 5-FAM probe and 260 fM (8.6 pg./mL) with the Cy5 probe. No sample preconcentration and complex pretreatments are required. Average fluorescence amplifications of 160 and 4500 are measured in the 5-FAM and Cy5 channel, respectively. These results are reasonably consistent with those worked out by FDTD simulations. The implementation of the proposed approach in multiwell-plate-based bioassays would lead to either signal redundancy (two dyes for a single analyte) or to a simultaneous detection of two analytes by different dyes, the latter being a key step toward high-throughput analysis.

Metal–Dielectric Interfacial Engineering with Mesoporous Nano-Carbon Florets for 1000-Fold Fluorescence Enhancements: Smartphone-Enabled Visual Detection of Perindopril Erbumine at a Single-molecular Level

“…These studies unambiguously pointed to the advantages of the engineered morphologies with sharp edges (such as nanostars, nanoprims, and nanorods) and their hierarchical assemblies for providing high electromagnetic (EM) field confinement, leading to enhanced SPCE. − Our earlier studies in this direction contributed to this by reaffirming the structural advantages of nanovoids and nano-cavities for achieving significant plasmon-based enhancements. − These, in turn, have been utilized for ultrasensitive and reliable analytical detection through both vibrational Raman (SERS) and fluorescence (SPCE). − Furthermore, 118-fold SPCE enhancements have been demonstrated by minimizing Ohmic losses using high refraction index dielectrics in conjugation with metal nanostructures . In spite of such significant advancements in both fundamental aspects and the applications thereof, the major challenges in SPCE enhancements using metallic nanostructures have been (i) inevitable Ohmic losses along with radiative damping, ,, (ii) poor chemical stability, especially in real-time applications, ,, and (iii) extensive isotropic photon scattering that compromises the magnitude of SPCE enhancements. − As opposed to the variety of metal, non-metallic, dielectric, two-dimensional, and zero-dimensional substrates that have been investigated for SERS, substrates for SPCE have been primarily restricted to metallic and their composites. ,, Thus, a ubiquitous platform that synergistically couples the plasmonic advantages of metallic nanostructures while simultaneously minimizing the Ohmic and radiative losses is desirable for improving the quality factor and reliability of SPCE, thereby transforming it into a powerful ultrasensitive analytical technique. − Achieving this would provide distinct opportunities for portable and mobile phone-based detection capabilities catering to the internet-of-things. , …”

Aptamer-Based Electrochemical Microfluidic Biosensor for the Detection of Cryptosporidium parvum

“…Several studies have investigated the use of electrodes modified with conductive nanostructures. For example, ice-crystal-like gold nanostructure has been used for the detection of the Enterococcus faecalis genome, , and the tunable plasmonic features of a nanostructured gold surface have been used to capture Plasmodium falciparum. , Despite the great potential of these biosensors for POC settings, previously reported assays are prone to cross-contamination as the electrode surface is directly exposed to the environment. Additionally, multiplexity remains an under-discussed topic, as even with multiple WEs incorporated into the device, they are only used for additional features like measuring voltage and current.…”

Plasmonic Nanomaterials for Colorimetric Biosensing: A Review

“…In particular, plasmonic nanomaterials are of great interest in applications that would benefit from a strong enhancement and confinement of the electromagnetic fields at subwavelength scale [7]. For instance, plasmonic nanomaterials are already conveniently adopted in Raman and fluorescence spectroscopy to achieve signal amplifications up to several orders of magnitude [8][9][10][11][12][13][14].…”