Localized Surface Plasmon Resonance Phenomenon Research Articles

Exploring the thermal and optical characteristics of Ti3C2 MXene for enhanced photothermal conversion

Ti3C2 MXene, a member of the two-dimensional (2D) transition metal carbides family, has garnered significant attention for its exceptional photothermal properties. To understand the mechanistic underpinnings of this feature, we conducted a comprehensive first-principles density functional theory analysis. This study was aimed at investigating the electronic band structure and vibrational characteristics of Ti3C2 MXene to unravel its microscopic process of photothermal conversion. After obtaining its optical and thermal properties, the process by which the material moves from light absorption to heat release is elucidated. The presence of localized surface plasmon resonance (LSPR) effects in Ti3C2 is proved by Finite-difference time-domain (FDTD) simulations. The synergy between the high thermal conductivity network in the Ti layers and the LSPR phenomenon is believed to be responsible for the superior photothermal conversion capabilities. This investigation enhances the understanding of the intrinsic properties of Ti3C2 MXene, confirming its status as an ultrahigh photothermal conversion material.

Near infrared photothermal inactivation of Candida albicans assisted by plasmonic nanorods

The use of photothermal processes has been proven effective in the control of microbial infections. Simultaneously, the localized surface plasmon resonance phenomena in metallic nanoparticles have been explored as an alternative strategy to achieve highly efficient localized heating. In this work, we propose the use of selected nanoheaters to improve the efficiency of fungal photothermal inactivation of Candida albicans through size optimization of plasmonic gold nanorods. Here, the optical heating of polyethylene glycol coated gold nanorods of varying sizes is evaluated, both theoretically and experimentally. A size-dependent computational approach was applied to identify metallic nanorods with maximized thermal performance at 800 nm, followed by the experimental comparison of optimal and suboptimal nanoheaters. Comparison among samples show temperatures of up to 53.0 °C for 41×10 nm gold nanorods against 32.3 °C for 90×25 nm, a percentage increase of ∼63% in photothermal inactivation assessments. Our findings reveal that gold nanorods of 41×10 nm exhibit superior efficiency in near-infrared (800 nm) photothermal inactivation of fungi, owing to their higher light-thermal conversion efficiency. The identification of high performance metallic nanoheaters may lead to the reduction of the nanoparticle dose used in plasmonic-based procedures and decrease the laser exposure time needed to induce cell death. Moreover, our results provide insights to better exploit plasmonic nanoparticles on photothermal inactivation protocols.

Four-core fiber-based multi-tapered WaveFlex biosensor for rapid detection of Vibrio parahaemolyticus using nanoparticles-enhanced probes.

Infections caused by Vibrio parahaemolyticus (V. parahaemolyticus) can be highly fatal, making rapid and sensitive detection of them is essential. A new optical fiber biosensor based on localized surface plasmon resonance (LSPR) phenomenon is developed in this paper. A tapered-in-tapered fiber structure based on MFM is constructed by using four-core fiber (FCF) and multi-mode fiber (MMF) to qualitatively detect different concentrations of V. parahaemolyticus. The sensor successfully excites the LSPR phenomenon and increases the attachment point of biomolecules on the probe surface by fixing gold nanoparticles (AuNPs), molybdenum disulfide nanoparticles (MoS2-NPs) and cerium dioxide nanorods (CeO2-NRs). The functionalization of polyclonal antibodies on the probe surface can improve the specificity of the sensor. The linear detection range of the developed sensor was 1 × 100-1 × 107 CFU/mL, the sensitivity was 1.61 nm/[CFU/mL], and the detection limit was 0.14 CFU/mL. In addition, the reusability, reproducibility, stability, and selectivity of the sensor probe are also tested, which shows that the sensor has great application prospects.

Double Polarization Peak Shift Sensitivity (DPPSS): An interrogation technique for a PCF SPR sensor

This research article provides a comprehensive analysis of a localized surface plasmon resonance (LSPR) based sensor, which operates in the visible to near-infrared region and uses a distinctive combination of two metals, ITO and Au as the plasmonic layers to achieve exceptional sensitivity. The wavelength spectrum that this sensor can now measure has been extended by combining these two materials in the RI region of 1.30 to 1.41, allowing the sensor to function in diverse fields such as bioimaging, biosensing, photocatalysis etc. A distinct and novel characteristic of the sensor which is termed as double polarization peak shift sensitivity (DPPSS) is proposed in this manuscript indicating the detection of resonance peak shift in both x-pol and y-pol simultaneously. DPPSS serves as the evaluative parameter for assessing the performance of the sensor. After optimizing all the structural parameters of the proposed sensor on the basis of DPPSS, it is found that the ultimate DPPSS value is 19560 nm/RIU and the maximum wavelength sensitivity is 19630 nm/RIU. Along with having a great sensitivity, the suggested sensor is fabrication friendly. The proposed research serves as a foundation for a thorough exploration of the LSPR phenomena for PCF in double metal scenario.

Atomic layer deposition of Pt nanoparticles using dimethyl (N, N–dimethyl-3-butene-1-amine−N) platinum and H2 reactant and its application to 2D WS2 photodetectors

2D transition metal dichalcogenides (2D TMDCs) have thin and flexible structures and can be widely applied to nanoelectronics technology as a representative of 2D materials. Research studies on the surface functionalization of 2D TMDCs with nanoparticles have been actively conducted for fabrication of high-performance devices. Specifically, platinum (Pt) has attracted significant attention as a surface functionalization material in various applications, including photosensors, biosensors, and gas sensors due to its effective catalytic effect and excellent corrosion resistance. However, solution-based methods and PVD technologies, widely used for Pt nanoparticle synthesis, have difficulties forming fine particles dispersed on nanomaterials. Atomic layer deposition (ALD) is emerging as an advantageous method for forming nanoparticles, and dimethyl (N,N-dimethyl-3-buten-1-amine-N) platinum (DDAP) can overcome disadvantages of conventional ALD Pt precursors. In this study, we successfully synthesized Pt films using hydrogen as a new reactant in the DDAP-based ALD Pt process and evaluated formation of nanoparticles on SiO2/Si substrates. Subsequently, the ALD Pt-functionalized photodetector was fabricated with 2D WS2, a representative visible-light photodetector material, and improvement of photocurrent was confirmed by providing additional carriers via the localized surface plasmon resonance phenomenon. Furthermore, preferentially growing at high surface energy points, such as defects on WS2 nanosheets, can suppress the capture of photoexcited electrons by defects, consequently extending the carrier lifetime and preventing surface oxidation of the device. In the wavelength range of 500–1200 nm, the photoresponsivity of the ALD Pt-functionalized WS2 photodetector was improved more than 10–20 times compared to pristine WS2, and the response time was also noticeably improved. This study presents a novel approach to Pt functionalization using ALD, opening new possibilities for advanced nanodevice applications.

AuNPs/GO Coated U-Shape Polished SMF Based Localized SPR Sensor for Musta’mal Water Identification

Potential of hybrid gold nanoparticles/graphene oxide (AuNPs/GO) coated single mode fiber (SMF) sensor by exploiting localized surface plasmon resonance (LSPR) effect for Musta’mal water identification was studied. Three structure shapes of fiber optics such as straight-shape, loop-shape and u-shape had been prepared. Three layers of AuNPs with 50 nm in diameter were drop-casted onto the partially unclad polished single mode fiber (SMF) to observe the maximum sensitivity of LSPR. To enhance the LSPR effect, one layer of GO was deposited on top of the AuNPs layer. Two optical light sources with least attenuation (1310 nm and 1550 nm) were employed to study the optical power output as the sensor immersed in different type of water samples. The u-shape SMF portrayed the maximum output power about 24.2 dBm at 1550 nm wavelength. According to the analysis, the deployment of 1550 nm laser wavelength resulted in better sensitivity with 23.2% improvement compared to 1310 nm wavelength. Apparently, the LSPR phenomenon created by AuNPs/GO able to enhance the plasmonic signal up to 51.9% than the uncoated SMF. The thinnest diameter of SMF’s cladding, d=0.1195 mm with U-shape structure exhibited the highest power different of 1.10 dBm, in which suggested the best sensing performance. In conclusion, the optimization of AuNPs/GO u-shape polished SMF resulted in the maximum sensitivity with value of S=72.7 dBm/RIU for Musta'mal water identification.

Super-resolution imaging for the detection of low-energy ion tracks in fine-grained nuclear emulsions

We propose a new wide-field imaging method that exploits the Localized Surface Plasmon Resonance phenomenon to produce super-resolution images with an optical microscope equipped with a custom design polarization analyzer module. In this paper we describe the method and apply it to the analysis of low-energy carbon ion tracks implanted in a nuclear emulsion film. The result is then compared with the measurements of the same tracks carried out at an electronic microscope. The images set side by side show their close similarity. The resolution achieved with the current microscope setup is estimated to be about 50 nm.

Synthesis Optimization and Antibacterial Performance of Colloidal Silver Nanoparticles in Chitosan

Colloidal silver nanoparticles were successfully synthesized via the chemical reduction method. The synthesis used AgNO3 as the precursor, chitosan as the reducing and stabilizing agents, and NaOH as the accelerator. The synthesis parameters were optimized. The samples were tested with a UV-vis spectrophotometer to observe their localized surface plasmon resonance (LSPR) phenomenon, a transmission electron microscope (TEM), and a particle size analyzer (PSA) to investigate their particle shape and size distribution. Further, silver nanoparticles were tested for their storage stability and antibacterial performance. The UV-vis spectroscopy data exhibited that the silver nanoparticles have been successfully synthesized, validating via the emergence of the LSPR absorption band at 402–418 nm. At 50 °C, the optimum synthesis was achieved for 100 min of reaction time by adding 0.033 M NaOH and AgNO3 4.00% (w/w, AgNO3/chitosan). TEM results showed spherical silver nanoparticles of 1–8 nm, while the PSA results exhibited particles sizes of about 12–59 nm. The colloidal silver nanoparticles were stable in storage for 8 weeks and had good antibacterial performance against E. coli, S. aureus, extended-spectrum beta-lactamases (ESBL), and methicillin-resistant S. aureus (MRSA). Therefore, colloidal silver nanoparticles have the potential as a material for medical applications.

Synthesis of Colloidal Silver Nanoparticles Using Alginate as Reducing and Stabilizing Agents and its Application as Antibacterial Material

Synthesis of colloidal silver nanoparticles has been successfully conducted through the chemical reduction technique. The synthesis used AgNO3, NaOH, and alginate as the precursor, accelerator reagent, and reducing agent and stabilizer, respectively. The effects of heating temperature, reaction time, accelerator concentration, and precursor concentration were investigated according to the localized surface plasmon resonance (LSPR) phenomenon using a UV-Vis spectrophotometer. The nanoparticle size distribution was observed via a Particle Size Analyzer (PSA). The stability of silver nanoparticles was studied for 8 weeks based on the LSPR phenomenon. Then, their antibacterial performance toward S. Aureus ATCC 25923 and E. Coli ATCC 25922 was examined. The results showed the absorbance intensities representing the number of silver nanoparticles formed were influenced by temperature, reaction time, NaOH concentration, and AgNO3 concentration. At 50°C heating, the optimum synthesis of silver nanoparticles was achieved at 50 min with a NaOH concentration of 0.013M. The higher AgNO3 concentration resulted in a greater concentration of silver nanoparticles produced. From the PSA characterization, the average particle sizes for the samples were 1.82 nm and 1.30 nm for AgNO3 concentrations (% w/w; AgNO3/Alginate) of 1.6% and 2.4%, respectively. Based on the LSPR phenomenon, colloidal silver nanoparticles were stable in storage for 8 weeks at room temperature. The increase in the concentration of silver nanoparticles within colloidal could enhance antibacterial performance against S. Aureus and E. Coli. Accordingly, silver nanoparticles synthesized with alginate as a stabilizer have the potential as an antibacterial compound for medical applications.

Localize surface plasmon resonance of silver nanoparticles using Mie theory

In this work, the optical properties of silver nanoparticles (AgNPs) were explored using Mie theory compared with the experimental AgNPs using the chemical reduction method. Mie’s theory is suited for accurately evaluating the scattering, absorption, and extinction cross-sections of spherical AgNPs. Therefore, the wavelength of localized surface plasmon resonance (LSPR) in the optical spectra of the spherical AgNPs was calculated. The experimental AgNPs have a spherical shape with an average particle size of 30 nm. In addition, the crystalline structure of AgNPs was found to be cubic with fcc structure with lattice constant a= 4.155 Å. Moreover, the excitation of the LSPR of the AgNPs was simulated using the finite-difference time-domain (FDTD) method at different wavelengths to explore the LSPR phenomena. The results show that spherical AgNPs are the most widely used materials in biosensors, biomedicine, optoelectronic devices, and solar cells due to their surface plasmon resonances in the visible spectrum region.

Plasmon-induced hot-electron injection effect: mechanism of performance enhancement for ZnO MSM hybrid photodetector by introducing Ag NWs and MXene

In this paper, a performance-enhanced hybrid ultraviolet metal–semiconductor–metal photodetector (UVPD) has been produced. This device incorporates a mixed photosensitive layer consisting of MXene nanoflakes that are covered on a thin film formed by Ag nanowires (NWs) wrapped in ZnO nanoparticles. This configuration, referred to as ZnO@Ag NWs/Mxene, capitalizes on the hot electrons generated by the localized surface plasmon resonance phenomenon occurring in the Ag NWs and MXene. These hot electrons possess sufficient energy to traverse the interface depletion layer and reach the ZnO layer. Therefore, the injected hot electrons serve as additional photo carriers in the ZnO layer, thereby increasing the number of photo-generated carriers and improving the carrier concentration in ZnO. The improved UVPD device exhibits an amplified photocurrent of ∼2499.35 nA at 5 V, under a light intensity of 6.52 mW cm−2 and a wavelength of 365 nm. Simultaneously, it achieves enhanced performance indices, including an On/Off ratio of ∼984.19, a responsivity (R p) of ∼66.87 mA W−1, and a detectivity (D *) of ∼1.82 × 1011 jones. These values represent a significant improvement compared to devices based solely on the ZnO configuration, with enhancements of ∼24.90, 3.93, 23.38, and 9.33 times, respectively. Based on the obtained results, it can be inferred that employing the hot electron injection effect to design and enhance the performance of optoelectronic devices based on wide band gap semiconductors is a reasonable and effective strategy.

Visible light photo-Fenton degradation of p-nitrophenol on Ag/Fe3O4/WO3 nanocomposites: Experimental and molecular dynamics investigations

The present research combines the adsorption behavior of phases in an aqueous medium with their band gap information for constructing a composite photo-Fenton catalyst that degrades para-nitrophenol (PNP). Thus, a series of Ag/ Fe3O4/WO3 Z-scheme photocatalysts were investigated for photo-Fenton PNP degradation. Classical MD simulations predicted effective H2O2 interaction with the photocatalyst's reduction (Fe3O4) part. The decoration of the composite surface by fine Ag nanostructures enhanced the visible light absorption efficiency of the photocatalyst through the localized surface plasmon resonance phenomenon. Photo-Fenton activities of Fe3O4/WO3 composites changed with their Ag loading. The composite with five-weight percent Ag loading demonstrated the best PNP degradation activity. The photoexcitation of Ag/Fe3O4/WO3 photocatalyst results in the accumulation of electrons on the CB of Fe3O4 and holes on the VB of WO3. The H2O2 molecules adsorb on the Fe3O4 part and are reductively cleaved to produce hydroxyl radicals, oxidizing PNP molecules nearby.

Synthesis and optical properties of Ag/Au-TiO2 plasmonic composite thin films

In this work, composite thin films based on titanium dioxide and noble metal nanoparticles (Ag, Au and bimetallic Ag/Au alloys) (Me-TiO2) were synthesized using the RF magnetron sputtering technique. The obtained thin films were characterized by TEM, SEM, XRD analysis, and Raman spectroscopy. It was observed that annealing in an argon atmosphere led to the crystallization of the initially amorphous as-deposited TiO2 matrix. The analysis of transmission spectra revealed that the composite thin films exhibited two light absorption regions: the first is local minima in the visible range associated with localized surface plasmon resonance (LSPR) phenomena; the second is light absorption due to the energy band gap. The study demonstrates the possibility of tuning these parameters in the composite films by changing the composition of the metal NPs. The LSPR minima for Ag-TiO2 and Au-TiO2 films were located at about 485 nm and 606 nm, respectively. In the composite thin films with bimetallic ∼Ag0.54/Au0.46 alloy nanoparticles, the position of the absorption peak was found to be at 555 nm. The energy band gap of these films also varies almost linearly, decreasing with an increase in the Au content, so that the largest value among the annealed Me-TiO2 composites was observed for the Ag-TiO2.

Preparation and characterization of VO2/Cu-Zr NPs/VO2 composite films with enhanced thermochromic properties

The contradiction between luminous transmittance (Tlum) and solar modulation ability (ΔTsol) of vanadium dioxide (VO2) smart windows can be reconciled through the regulation of surface morphology. In this study, Cu-Zr bimetallic nanoparticles (Cu-Zr NPs) were embedded into VO2/VO2 bilayer films by pulsed laser deposition to tailor the VO2 surface morphology. XRD characterization revealed that the introduction of Cu-Zr NPs can significantly improve the crystallinity of VO2 films. FESEM characterization illustrated that the grain size and morphology of top-VO2 layer were sensitive to the density of Cu-Zr NPs. From the transmission spectrum, evident localized surface plasmon resonance (LSPR) phenomena could be observed in the range of 1300–1500 nm. When the pulse number for depositing Cu-Zr NPs is 35, the composite film exhibits both high Tlum of 62.4% and excellent ΔTsol of 10.6% simultaneously. In addition, the finite difference time domain (FDTD) simulation suggested that the improvement of thermochromic properties could be attributed to the LSPR effect induced by the unevenly distributed VO2 grains on the surface. This work confirmed the existence of non-noble Cu-Zr NPs could both improve the crystallinity and regulate the surface morphology of VO2 film, which simplified the fabricating process of VO2 thermochromic smart windows and was cost-effective.

Specific Instantaneous Detection of Klebsiella pneumoniae for UTI Diagnosis with a Plasmonic Gold Nanoparticle Conjugated Aptasensor.

Urinary tract infection (UTI), which can be caused by various pathogens, if not detected at an early stage can be fatal. It is essential to identify the specific pathogen responsible for UTI for appropriate treatment. This study describes a generic approach to the fabrication of a prototype for the noninvasive detection of a specific pathogen using a tailor-made plasmonic aptamer-gold nanoparticle (AuNP) assay. The assay is advantageous because the adsorbed specific aptamers passivate the nanoparticle surfaces and reduce and/or eliminate false-positive responses to nontarget analytes. Based on the localized surface plasmon resonance (LSPR) phenomena of AuNP, a point-of-care aptasensor was designed that shows specific changes in the absorbance in the visible spectra in the presence of a target pathogen for robust and fast screening of UTI samples. In this study, we demonstrate the specific detection of Klebsiella pneumoniae bacteria with LoD as low as 3.4 × 103 CFU/mL.

Localized Surface Plasmon Resonance-Based Nanosensor for Rapid Detection of Glyphosate in Food Samples

In this study, we developed a biosensor based on the localized surface plasmon resonance (LSPR) phenomenon of gold nanoparticles (AuNPs) to detect the widely used herbicide glyphosate in food samples. To do so, either cysteamine or a specific antibody for glyphosate were conjugated to the surface of the nanoparticles. AuNPs were synthesized using the sodium citrate reduction method and had their concentration determined via inductively plasma coupled mass spectrometry. Their optical properties were analyzed using UV-vis spectroscopy, X-ray diffraction, and transmission electron microscopy. Functionalized AuNPs were further characterized via Fourier-transform infrared spectroscopy, Raman scattering, Zeta potential, and dynamic light scattering. Both conjugates succeeded in detecting the presence of glyphosate in the colloid, although nanoparticles functionalized with cysteamine tended to aggregate at high concentrations of the herbicide. On the other hand, AuNPs functionalized with anti-glyphosate functioned at a broad concentration range and successfully identified the presence of the herbicide in non-organic coffee samples and when it was added to an organic coffee sample. This study demonstrates the potential of AuNP-based biosensors to detect glyphosate in food samples. The low-cost and specificity of these biosensors make them a viable alternative to current methods for detecting glyphosate in foodstuffs.

Comparison study of the structure, dielectric function, and two-photon absorption cross-section of BiOI and Ag/BiOI nanomaterials

In this research, the interesting methods including X-ray diffraction (XRD) pattern, Field Emission Scanning Electron Microscopy (FESEM) images, energy dispersive X-ray (EDX), UV–Vis spectroscopy, Diffuse reflectance (DRS) spectrum, KK method, and Z-scan measurements were employed for characterizations of prepared BiOI and Ag/BiOI nanomaterials. The optical indices such as n, k, and ε1 and ε2 were assessed based on reflectance spectra data and the Kramers-Kronig (KK) method. Furthermore, the nonlinear optical (NLO) properties of prepared BiOI and Ag/BiOI nanomaterials in different Ag precents were examined through the Z-scan method using the laser beam at 532 nm wavelength. The two-photon absorption (TPA) and self-focusing performance are revealed by the prepared nanomaterials. Adding Ag into BiOI structures, significantly increases the TPA cross-section, σ2 which reaches up to 1.14578 × 10−21 cm4/W for the sample of S3. One of the significant factors that affected the improvement of the optical nonlinearity properties of Ag/BiOI and over BiOI was ascribed to the combined consequence of Ag's localized surface plasmon resonance (LSPR) phenomena, resulting in improved light absorption intensity coupling interaction, significant photo-produced electron-hole separability, and prolonged carrier lifetime.

Influence of Ag NPs shape and metal oxide shell embedded in the active layer of Si-based hybrid plasmonic solar cells on device efficiency

In this research, via embedding the plasmonic metallic nanostructure of dome shape Ag coated with MoO3 in the active layer of a hybrid Si solar cell, the device efficiency significantly improved. The effect of Ag nanostructures shape and metal oxide coated material implanted in Poly (3,4-ethylenedioxythiophene:Poly (styrenesulfonate)/c-Si (PEDOT:PSS) as an active layer of hybrid solar cells (HSC) on improvements of photocurrent was extensively investigated. HSC with an Ag nanodome shape and MoO3 shell showed an open circuit voltage (Voc) of 0.88 V, an electrical short circuit current density (Jsc) of 38.42 mA cm−2, and a fill factor (FF) of 0.82. The energy conversion efficiency was considerably increased from 15.60% for HSC solar cells having nanopyramid Ag with SiO2 shell to 28.02% for nanodome Ag with MoO3 shell. The localized surface plasmon resonance (LSPR) phenomenon, photogenerated charge recombination, and incident photon scattering and absorption behavior all contribute to this improvement.

Humanoid shaped optical fiber plasmon biosensor functionalized with graphene oxide/multi-walled carbon nanotubes for histamine detection.

Histamine is a biologically active molecule that serves as a reliable predictor of the quality of fish. In this work, authors have developed a novel humanoid-shaped tapered optical fiber (HTOF) biosensor based on the localized surface plasmon resonance (LSPR) phenomenon to detect varying histamine concentrations. In this experiment, a novel and distinctive tapering structure has been developed using a combiner manufacturing system and contemporary processing technologies. Graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) are immobilized on the HTOF probe surface to increase the biocompatibility of biosensor. In this instance, GO/MWCNTs are deployed first, then gold nanoparticles (AuNPs). Consequently, the GO/MWCNTs help to give abundant space for the immobilization of nanoparticles (AuNPs in this case) as well as increase surface area for the attachment of biomolecules to the fiber surface. By immobilizing AuNPs on the surface of the probe, the evanescent field can stimulate the AuNPs and excite the LSPR phenomena for sensing the histamine. The surface of the sensing probe is functionalized with diamine oxidase enzyme in order to enhance the histamine sensor's particular selectivity. The proposed sensor is demonstrated experimentally to have a sensitivity of 5.5 nm/mM and a detection limit of 59.45 µM in the linear detection range of 0-1000 µM. In addition, the probe's reusability, reproducibility, stability, and selectivity are tested; the results of these indices show that the probe has a high application potential for detecting histamine levels in marine products.

Improving the selective naked-eye detection of COVID-19 mediated by simultaneously using three different target oligonucleotides coated on plasmonic AuNPs/hexagonal Ag@AuNPs

The localized surface plasmon resonance (LSPR) phenomenon provides a versatile property in biosensor technology. This uncommon feature was utilized to produce a homogeneous optical biosensor to detect COVID-19 by the naked-eye readout. In this work, we synthesized two types of plasmonic nanoparticles: (i) AuNPs and (ii) hexagonal core-shell nanoparticles-Au shell on AgNPs (Au@AgNPs). We report herein the development of two colorimetric biosensors employing the efficient targeting and the binding ability for three regions of the COVID-19 genome, that is, S-gene, N-gene and E-gene, at the same time. Two AuNPs and Ag@AuNPs individually coated with three different targets oligonucleotide sequence (TOs) (AuNPs-TOs-mix and Ag@AuNPs-TOs-mix) for simultaneous detection of S-gene, N-gene and E-gene of the COVID-19 virus, using the LSPR and naked-eye methods in the laboratory and biological samples. The target COVID-19 genome RNA detected using the AuNPs-TOs-mix and Ag@AuNPs-TOs-mix can achieve the same sensitivity. The detection ranges by the AuNPs-TOs-mix and Ag@AuNPs-TOs-mix are both sufficiently improved in equal amounts in comparison to any of the AuNPs-TOs and Ag@AuNPs-TOs. The sensitivity of the current COVID-19 biosensors were 94% and 96% based on the number of positive samples detected for AuNPs-TOs-mix and Ag@AuNPs-TOs-mix, respectively. Moreover, all the real-time PCR confirmed negative samples obtained the same results by the biosensor; accordingly, the specificity of this approach got to 100%. The current study reports a selective, reliable, reproducible and visual ‘naked-eye’ detection of COVID-19, devoid of the requirement of any sophisticated instrumental techniques.Communicated by Ramaswamy H. Sarma