Longitudinal Surface Plasmon Resonance Research Articles

Gold Nanobipyramids as Plasmonic Sensor for Insecticide Detection in Lettuce

The application of malathion, an insecticide derived from organophosphates, raises substantial apprehensions over human health in the context of pest management in agricultural produce. The presence of a lack of specialized knowledge and the intricate nature of traditional diagnostic methods have further intensified these symptoms, resulting in significant and persistent damage to the human body. The present study aims to synthesis a gold-nanobipyramids (AuNBPs) for identifying malathion and other organophosphate pollutants, even at exceedingly low levels of detection. The AuNBPs is synthesis by the utilization of the seed-mediated growth (SMG) method. The UV-Vis spectroscopy analysis has identified 2 unique absorption peaks, specifically transverse surface plasmon resonance (t-SPR) occurring between 550 and 600 nm, and longitudinal surface plasmon resonance (l-SPR) occurring within the wavelength range of 750 to 850 nm. Additional analysis of AuNBPs reveals its capacity for notable and distinctive optical resonance, particularly in the visible and near-infrared regions of the electromagnetic spectrum. This characteristic renders AuNBPs very appropriate for the development of localized surface plasmon resonance (LSPR) sensors. The sensitivity experiments conducted on the LSPR sensor based on AuNBPs have shown compelling evidence of its capability to detect malathion and other pollutants in the AuNBPs growth solution across different concentrations. These findings highlight the sensor’s potential for efficient residue detection of malathion. This discovery underscores the significant importance of its function in safeguarding food safety and reducing the potential hazards linked to the utilization of malathion and other insecticides based on organophosphates in agricultural practices. HIGHLIGHTS The present study reports a gold-nanobipyramids (AuNBPs) synthesis using the seed-medited growth technique and characterized using a range of techniques, including UV-Vis spectroscopy and XRD The plasmonic sensor demonstrated heightened sensitivity to malathion, as evidenced by a rise in values corresponding to the concentration of the residual solution The intensity of AuNBP in the presence of malathion was significantly increased compared to that in deionized water, suggesting that AuNBP exhibits a strong and effective reaction to the presence of malathion residue GRAPHICAL ABSTRACT

Strong coupling between plasmonic nanocavity gold nanorods and quantum dots emitter

The discovery of hybrid states in strong coupling interaction has gained growing attention in cavity-quantum electrodynamics research owing to its fundamental directives and potential in advanced optical applications. The ultra-confined mode volume of plasmonic cavity gold nanorods (AuNRs), particularly at the nanorod tip “hotspot” provides a large coupling strength, a prerequisite for a coherent energy exchange in the strong coupling regime. Here, we reported a remarkable Rabi splitting of ∼231 meV between gold nanorods longitudinal localized surface plasmon resonance (LLSPR) mode and quantum dots (QDs) at ambient conditions, monitored by dielectric medium tuning. Numerical simulations confirmed the result, displaying absorption spectral splitting.

A multicolor aptasensor based on target-induced anti-etching gold nanorod for visible detection of aflatoxin B1

Foods contaminated with aflatoxin B1 (AFB1) pose a serious threat to humans, so rapid and sensitive detection of AFB1 plays an important role in public health. In this work, we developed a multicolor aptasensor based on target-mediated anti-etching of gold nanorods (AuNRs) for on-site visible detection of AFB1. The target was used as a competitor that competed with a cDNA probe labeled by horse radish peroxidase (cDNA-HRP) to bind with the aptamer coated in a microplate. The sensing mechanism was based on regulating the etching process of AuNRs upon the addition of different concentrations of AFB1. In the absence of AFB1, the AuNRs solution undergoes a distinct change from red to pink due to the etching effect of TMB2+ generated by a specific redox reaction catalyzed by the cDNA-HRP. However, in the presence of AFB1, the specific binding between AFB1 and aptamer made cDNA-HRP free out of the microplate, inhibiting the etching of AuNRs. Consequently, a redshift of longitudinal localized surface plasmon resonance (LSPR) and color alterations can be observed along with increasing the concentration of AFB1. The LSPR for visual estimation limits were 0.46 ng/mL. A good linear relationship between the wavelength shift and the concentration of AFB1 was achieved from violet to light green in the range of 1–1000 ng/mL. The established aptasensor displayed excellent detection performance, which was suitable for on-site analysis of AFB1 in actual food samples, and provided a new idea of immediate visualization detection for food hazardous factors.

Weak plasmonic photocatalysis in unsupported colloidal gold nanorods

Metal-semiconductor plasmonic nanosystems have the ability to extract photocarriers generated on colloidal gold nanoparticles efficiently through the Schottky junction. This process leads to effective visible light photocatalysis. However, due to the short lifespan of plasmon carriers, plasmonic loss occurs before extraction by the semiconductor and transfer to the adsorbent. We aim to investigate the direct transfer of plasmonic energy to adsorbed organic pollutants in visible light photocatalysis using unsupported colloidal gold nanorods (Au NRs). Our decision to use gold nanorods is based on their exceptional ability to harness a greater amount of visible light through their longitudinal surface plasmon resonance (LSPR) at 765 nm and transverse surface plasmon resonance (TSPR) band at 521 nm. Additionally, we conducted experiments to evaluate the photocatalytic capabilities under specific wavelengths, such as blue (405 nm), green (532 nm), and red (660 nm) lasers, to gain a better understanding of the -d-sp interband transition and the role of surface plasmon in photocatalysis. Surprisingly, unsupported Au NRs showed only weak plasmonic photocatalysis under all these excitations. With the help of supporting characterization tools, we observed that without semiconductor support, the photoexcited carriers over Au nanorods are not well separated, resulting in reduced photocatalysis.

Influence the diphenhydramine hydrochloride–sodium carboxymethyl cellulose complex for nanoaggregate formation

This study aimed to create nanoaggregates that improve the synergistic interaction between the opposing charges in drug-polyelectrolyte complexes. In this study, sodium carboxymethyl cellulose (NaCMC) polyelectrolytes and diphenhydramine hydrochloride (DPC) drug molecules were used to form the nanoaggregate. The aggregation behaviour of NaCMC-DPC complexes was determined by using conductivity methods. The critical micelle concentrations (CMC) of NaCMC were reduced from 0.737 to 0.337 g/l in the aqueous and 29.18 mg/l in the DPC. The modified Corrin and Harkins (CH) and Frahm's approaches evaluated the binding efficiency of the NaCMC-DPC interaction. NaCMC-DPC complexes were examined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques to conform to the formation of bilayer vesicles. Furthermore, we prepared the silver nanoparticles by using NaCMC-DPC complex mixtures. We demonstrated how NaCMC-DPC mixtures might influence the self-assembly of silver nanochain designs that differed from open "end-to-end" networks. The results indicated that the assembly of silver nanochains was regulated by a variation of electrostatic interactions inside the NaCMC-DPC components, which organized themselves around anisotropic nanochains surfaces. Among the optical properties altered by the linear assembly, the longitudinal surface plasmon resonance band at 624 nm has an enhanced redshift.

Photothermal Actuation of Thick 3D-Printed Liquid Crystalline Elastomer Nanocomposites.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials that transduce an input energy into a mechanical response. LCE composites prepared with photothermal agents, such as nanoinclusions, are a means to realize wireless, remote, and local control of deformation with light. Amongst photothermal agents, gold nanorods (AuNRs) are highly efficient converters when the irradiation wavelength matches the longitudinal surface plasmon resonance (LSPR) of the AuNRs. However, AuNR aggregation broadens the LSPR which also reduces photothermal efficiency. Here, the surface chemistry of AuNRs is engineered via a well-controlled two-step ligand exchange with a monofunctional poly(ethylene glycol) (PEG) thiol that greatly improves the dispersion of AuNRs in LCEs. Accordingly, LCE-AuNR nanocomposites with very low PEG-AuNR content (0.01wt%) prepared by 3D printing are shown to be highly efficient photothermal actuators with rapid response (>60%strains-1) upon irradiation with near-infrared (NIR; 808nm) light. Because of the excellent dispersion of PEG-AuNR within the LCE, unabsorbed NIR light transmits through the nanocomposites and can actuate a series of samples. Further, the dispersion also allows for the optical deformation of millimeter-thick 3D printed structures without sacrificing actuation speed. The realization of well-dispersed nanoinclusions to maximize the stimulus-response of LCEs can benefit functional implementation in soft robotics or medical devices.

Dynamic Orientation Control of Gold Nanorods in Polymer Brushes by Their Thickness Changes for Plasmon Switching

AbstractGold nanorods (AuNRs) have unique optical properties such as transverse and longitudinal localized surface plasmon resonance (T‐ and L‐LSPR). As the L‐LSPR absorption depends on the angle of the AuNRs to incident light and polarization, orientational control of AuNRs is a crucial issue. In spite of various techniques to control AuNR orientation, dynamic orientation tuning on a solid substrate remains challenging. Herein, dynamic changes are demonstrated in AuNR orientation in the anionic polymer (DNA) brushes via control of their thickness by salt concentration. AuNRs vertically align toward the substrates when their thickness exceeds the AuNR length. Once their thickness becomes shorter than the AuNR length, the attached AuNRs begin to tilt. The tilt reaches a maximum level close to horizontal when the thickness decreases to half that of the AuNR length. The dynamic control between the vertical (uniform) and tilted (random) orientation of the AuNRs showed not only absorption intensity changes in L‐LSPR but also the switching of side‐by‐side plasmon coupling. The polymer brush‐based system affords a novel platform for the stimuli‐responsive control of AuNR orientation on the substrates via changes in the thickness of polymer brushes for actively tunable plasmonic substrates.

Gold nanomakura: nanoarchitectonics and their photothermal response in association with carrageenan hydrogels.

Photothermal conversion of light into heat energy is an intrinsic optical property of metal nanoparticles when irradiated using near-infrared radiation. However, the impact of size and shape on the photothermal behaviour of gold nanomakura particles possessing optical absorption within 600-700 nm as well as on incorporation in hydrogels is not well reported. In this study, nanomakura-shaped anisotropic gold nanoparticles (AuNMs) were synthesized via a surfactant-assisted seed-mediated protocol. Quaternary cationic surfactants having variable carbon tail length (n = 16, 14, 12) were used as capping for tuning the plasmon peak of gold nanomakura within a 600-700 nm wavelength. The aspect ratio as well as anisotropy of synthesized gold nanomakura can influence photothermal response upon near-infrared irradiation. The role of carbon tail length was evident via absorption peaks obtained from longitudinal surface plasmon resonance analysis at 670, 650, and 630 nm in CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM, respectively. Furthermore, the impact of morphology and surrounding milieu of the synthesized nanomakuras on photothermal conversion is investigated owing to their retention of plasmonic stability. Interestingly, we found that photothermal conversion was exclusively assigned to morphological features (i.e., nanoparticles of higher aspect ratio showed higher temperature change and vice versa irrespective of the surfactant used). To enable biofunctionality and stability, we used kappa-carrageenan- (k-CG) based hydrogels for incorporating the nanomakuras and further assessed their photothermal response. Nanomakura particles in association with k-CG were also able to show photothermal conversion, depicting their ability to interact with light without hindrance. The CTAB-AuNM, MTAB-AuNM, and DTAB-AuNM after incorporation into hydrogel beads attained up to ≈17.2, ≈17.2, and ≈15.7 °C, respectively. On the other hand, gold nanorods after incorporation into k-CG did not yield much photothermal response as compared to that of AuNMs. The results showed a promising platform to utilize nanomakura particles along with kappa-carrageenan hydrogels for enabling usage on nanophotonic, photothermal, and bio-imaging applications.

High yield seedless synthesis of mini gold nanorods: partial silver decoupling allows effective nanorod elongation with tunable surface plasmon resonance beyond 1000 nm and CTAB-free functional coating for mTHPC conjugation

This work reports on the one-pot synthesis of mini (d < 10 nm) gold nanorods, their effective elongation via a partial silver decoupling method to achieve a longitudinal SPR of >1000 nm and CTAB-free functional coating with mTHPC conjugation.

Application of Anisotropic Gold Nanomaterials in Plasmonic Sensors for Detection of Glyphosate

The trend of using agrochemicals is increasing, especially glyphosate-based herbicides (GBH). The application of toxic chemicals as pest control in food crops carries a risk to human safety. Therefore, it is important to create a sensor for detection through Localized Surface Plasmon Resonance (LSPR) by utilizing anisotropic gold nanoparticles (AGN) to detect the presence of GBH contaminants in the form of malathion and temephos, with a detection level as low as three-part per million (ppm). AGN-based LSPR is successfully synthesized through an experimental technique using the Seed Mediated Growth Method (SMGM). The UV-Vis response showed two strong absorbances with a peak occurring around 500 to 600 nm, the peak within the transverse surface plasmon resonance range (t-SPR) corresponds to one aspect, while the peak within the spectral range extending from 700 nm to 900 nm corresponds to another aspect, namely Longitudinal Surface Plasmon Resonance (l-SPR). Anlysis of the FESEM photograph shows a structure consisting of two particles with different shapes, pentagonal pyramids and a bone shape. Pentagonal pyramids joined with a surface density of 64.43 ± 1,53 % and bone shape of 32,46 ± 1.53 %. This characterization shows strong and distinctive optical resonance in the near-infrared visible light spectrum, which is very suitable for LSPR sensors. It is necessary to fabricate an LSPR sensor device capable of detecting the presence of GBH by testing sensitivity, stability and repeatability. The sensitivity test results were evaluated by varying the synthesis time and concentration of contaminants in the AGN growth solution. It confirmed that the AGN-based LSPR sensor has a promising potential for GBH residue detection.

Bottom-Up Then Top-Down Synthesis of Gold Nanostructures Using Mesoporous Silica-Coated Gold Nanorods.

Gold nanostructures were synthesized by etching away gold from heat-treated mesoporous silica-coated gold nanorods (AuNR@mSiO2), providing an example of top-down modification of nanostructures made using bottom-up methodology. Twelve different types of nanostructures were made using this bottom-up-then-top-down synthesis (BUTTONS), of which the etching of the same starting nanomaterial of AuNR@mSiO2 was found to be controlled by how AuNR@mSiO2 were heat treated, the etchant concentration, and etching time. When the heat treatment occurred in smooth moving solutions in round-bottomed flasks, red-shifted longitudinal surface plasmon resonance (LSPR) was observed, on the order of 10-30 min, indicating increased aspect ratios of the gold nanostructures inside the mesoporous silica shells. When the heat treatment occurred in turbulent solutions in scintillation vials, a blue shift of the LSPR was obtained within a few minutes or less, resulting from reduced aspect ratios of the rods in the shells. The influence of the shape of the glassware, which may impact the flow patterns of the solution, on the heat treatment was investigated. One possible explanation is that the flow patterns affect the location of opened pores in the mesoporous shells, with the smooth flow of solution mainly removing CTAB surfactants from the pores along the cylindrical body of mSiO2, therefore increasing the aspect ratios after etching, and the turbulent solutions removing more surfactants from the pores of the two ends or tips of the silica shells, hence decreasing the aspect ratios after etching. These new stable gold nanostructures in silica shells, bare and without surfactant protection, may possess unique chemical properties and capabilities. Catalysis using heat-treated nanomaterials was studied as an example of potential applications of these nanostructures.

Suppression of polarization instability in ultrashort Fabry–Pérot fiber laser

Due to the weak birefringence from the intracavity fiber, vector solitons are easily generated in GHz-fundamental-repetition-rate mode-locked fiber lasers, which can exhibit diverse time-varying polarization dynamics. These soliton dynamics can lead to polarization instability of the pulse train, which prevents industrial and scientific applications that require stable and uniform pulse trains. However, it is hard to suppress the polarization instability due to insufficient space for inserting traditional polarizers and difficulties in enhancing the fiber birefringence in the ultrashort fiber laser cavity. To this end, here we propose an alternative method that can effectively transform the vector solitons into scalar solitons by exploring gold nanorod (GNR) film as a polarizer in the laser cavity. First, the theoretical studies of polarization dynamics in ultrashort Fabry–Pérot (FP) fiber lasers with and without intracavity GNR film are conducted. The results indicate that the use of GNR film can significantly suppress the polarization instability and generate scalar solitons. Then, the large-scale preparation of GNRs with longitudinal surface plasmon resonance absorption peak of >1380 nm is realized by a two-step seed-mediated method, and the GNR film with an operation wavelength range covering the C + L band is fabricated by electrospinning. Finally, we apply the GNR film to a 2-cm-long FP fiber laser, and convert polarization rotation vector solitons to linearly polarized solitons (LPSs) at 1.5 μm. The polarization extinction ratio of the improved LPS pulse train is up to 33 dB.

Nanomechanical Photothermal Near Infrared Spectromicroscopy of Individual Nanorods.

Understanding light-matter interaction at the nanoscale requires probing the optical properties of matter at the individual nanoabsorber level. To this end, we developed a nanomechanical photothermal sensing platform that can be used as a full spectromicroscopy tool for single molecule and single particle analysis. As a demonstration, the absorption cross-section of individual gold nanorods is resolved from a spectroscopic and polarization standpoint. By exploiting the capabilities of nanomechanical photothermal spectromicroscopy, the longitudinal localized surface plasmon resonance in the NIR range is unraveled and quantitatively characterized. The polarization features of the transversal surface plasmon resonance in the VIS range are also analyzed. The measurements are compared with the finite element method, elucidating the role played by electron surface and bulk scattering in these plasmonic nanostructures, as well as the interaction between the nanoabsorber and the nanoresonator, ultimately resulting in absorption strength modulation. Finally, a comprehensive comparison is conducted, evaluating the signal-to-noise ratio of nanomechanical photothermal spectroscopy against other cutting-edge single molecule and particle spectroscopy techniques. This analysis highlights the remarkable potential of nanomechanical photothermal spectroscopy due to its exceptional sensitivity.

Curcumin-capped gold nanorods as optical sensing platform for sequence specific detection of DNA based on their self-assembly

We are reporting curcumin-induced gold nanorods as an optical sensing platform for the detection of sequence-specific DNA target through their self-assembly. The combined effect of eco-friendly reducing agent (i.e., curcumin) and silver nitrate in a basic medium (i.e., pH 10) has been attributed for the formation of small gold nanorods (AuNRs) having approximate length and diameter i.e., 19.7 ± 0.8 nm and 6.0 ± 0.5 nm, respectively, and lower longitudinal surface plasmon resonance (SPR) enable to detect and analyse different biomarkers. Further, for evaluating cellular uptake of as-synthesized AuNRs, the cytotoxicity study has been carried out by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay on A549 cells and HEPG2 cell lines, respectively, and shown approximately similar cytotoxicity. Interestingly, as-synthesized optically and electronically active AuNRs based nanobiosensing platform enable to detect sequence-specific DNA targets with low level of detection limit i.e., LOD 8.6 ± 0.15 pM for complimentary target (CT) DNA with higher sensitivity and better selectivity. Finally, this study is suggesting a simplistic bio-mediated approach of tuning the shape and size of AuNRs for sensitive, selective and reliable nanobiosensing platform for sequence-specific DNA detection related to cancer cells.

Transfers of the OAM and SAM densities of Bessel beam into the orbital and spin torques upon gold nanorod

The optomechanical interplay of a Bessel beam (an optical vortex) with a gold nanorod (GNR) in water is theoretically studied. The optical force and torque exerted on the GNR are analyzed using Maxwell's stress tensor to investigate the transfer rates of the orbital angular momentum (OAM) and the spin angular momentum (SAM) densities of Bessel beam into the orbital and spin torques upon GNR, respectively. From the numerical analysis, we find that the ratio of the orbital torque to the spin torque on the GNR matches the ratio of OAM to SAM of Bessel beam, corresponding to the order (topological charge) of the Bessel beam. This is to say that the transfer rate of the OAM density of Bessel beam into the orbital torque exerted on GNR nearly equals that of the SAM density into the spin torque. It implies that the spin-orbit interaction (SOI) of the optical vortex beam via a GNR is very weak. In addition, the spin torque is nearly equal to the corresponding zilch torque, the surface integral of Lipkin's zilch stress tensor. This could be because a GNR can be regarded as a perfect electric dipole particularly when the wavelength of the incident light is close to and little longer than the longitudinal surface plasmon resonance of GNR; the dipole's orientation is along the long axis of GNR. In contrast, the SOI via a spherical gold nanoparticle (GNP) is strong due to no preferred orientation for the equivalent dipole; a part of SAM of the optical vortex is transferred to the orbital torque upon GNP. Our results demonstrate that GNR, functioning as an ideal electric dipole, is a highly effective probe for detecting the OAM and SAM densities of an optical vortex individually through its distinct orbital and spin motions, without any crosstalk.

Combined Facile Synthesis, Purification, and Surface Functionalization Approach Yields Monodispersed Gold Nanorods for Drug Delivery Applications.

Synthesizing gold nanorods (AuNRs) by seed-mediated growth method results in the presence of undesired size and shape particles by-products occupying 10-90% of the population. In this study, AuNRs are synthesized by the seed-mediated growth method using cetyltrimethylammonium bromide (CTAB) as a surfactant. AuNRs with redshifted longitudinal localized surface plasmon resonance (LLSPR) peak, localized in the biological "transparency window" (650-1350nm), are synthesized after optimizing seed solution, silver nitrate solution, and hydrochloric acid solution volumes, based on the published protocols. A two-step purification method, dialysis followed by centrifugation, is applied to remove excess CTAB and collect LLSPR-redshifted AuNRs with high rod purity (>90%). CTAB is subsequently exchanged with polyethylene glycol (PEG) to improve AuNRs biocompatibility. PEGylated AuNRs are confirmed innocuous to both SN4741 cells and B16F10 cells by the modified MTT assay and the modified lactate dehydrogenase (LDH) assay up to 1nm and 24h incubation. In this study, a combined facile synthesis, purification, and surface functionalization approach is proposed to obtain water-dispersible monodispersed AuNRs for drug delivery applications.

Surface plasmon resonance effects of Ti3C2 MXene for degradation of antibiotics under full spectrum

The ML-(Ti1−X2+TiX3+)3C2VAlX(ML-Ti3C2) crystal was exfoliated into the crystal Ti3C2 MXene with coexistence of (Ti1−X2+TiX3+)3C2VAlX MXene and Ti2CVAlX MXene by HF etching Ti3AlC2 and ultrasonic crushing in water. Ti3C2 MXene exhibits the surface plasmon effects of transverse and longitudinal surface plasmon resonance due to its surface holes and internal bound electrons. When excited by the simulated sunlight, the high energy hot holes on the surface of plasma Ti3C2 MXene crystal directly oxidize the antibiotics and the organic pollutants. The electrons bound in the crystal lag behind the excitation of holes and migrate to the surface to further degradation. After 150 min of near infrared light irradiation, the degradation rates of tetracycline (TC) and ciprofloxacin (CIP) by Ti3C2 MXene are 78.91% and 99.26%, respectively. They are 1.35/1.00 and 1.53/3.11 times of ML-Ti3C2 and (001)TiO2/Ti3C2. This study indicates that Ti3C2 MXene has significant degradation effects on antibiotics in the full spectral range. Our work intends to provide a valuable reference for the design of the MXene full spectral photocatalyst.

Temperature-Derived Purification of Gold Nano-Bipyramids for Colorimetric Detection of Tannic Acid.

Gold nanostructures have attracted broad attention. Among various nanostructures, gold nanobipyramids have shown great potential in sensing, biomedicine, environmental protection, chemical catalysis, and optics due to their unique physical and optical properties and ease of chemical functionalization. Compared with other plasmonic nanostructures, gold nanobipyramids possess narrow optical resonances, stronger plasmonic local field enhancement, and size- and shape-dependent surface plasmon resonance. However, the synthesis and purification of homogeneous gold nanobipyramids are very challenging. The gold nanobipyramids synthesized via the commonly used seed-mediated growth method have low yields and are often coproduced with spherical nanoparticles. In this study, we reported a temperature-derived purification method for the isolation of gold bipyramids. In the presence of salt, by altering the temperature of the solution, large gold bipyramids can be separated from small spherical nanoparticles. As a result, a yield of as high as 97% gold nanobipyramids can be achieved through a single round of purification, and correspondingly, the ratio between the longitudinal surface plasmon resonance (LSPR) and transverse SPR intensity significantly increases to as high as 6.7. The purified gold nanobipyramids can be used as a colorimetric probe in the detection of tannic acid with a detection limit of 0.86 μM and a linear detection range from 1.25 to 37.5 μM.

Light-induced synthesis of silver nanoprisms as a surface-enhanced Raman scattering substrate for N-acetyl procainamide drug quantification

Triangle-shaped silver nanoprisms (AgNPMs) were prepared by a photo-induced method through a seed-mediated growth process and were successfully employed as an ultra-sensitive surface-enhanced Raman scattering (SERS) substrate for the detection of the chemotherapeutic N-acetyl procainamide (NAPA) compound. The transformation of the morphology of the nanoprisms substrate could be noted with a remarkable change in color, possessing an average size of 95 nm. The shape-modified AgNPMs exhibited interesting optical characteristics owing to the truncated dual edges, which led to a pronounced longitudinal localized surface plasmonic resonance (LLSPR) behavior. The nanoprisms-based SERS substrate demonstrated an outstanding sensitivity for NAPA in aqueous solutions with the lowest ever reported detection limit of 0.5 × 10−13 M corresponding to excellent recovery and stability. A steady linear response with a broad dynamic range (10−4–10−12 M) and an R2 of 0.945 was also achieved. The results proved that the NPMs demonstrated excellent efficiency, reproducibility (97%), and stability (30 days) with a superior Raman signal enhancement reaching an ultralow detection limit of 0.5 × 10−13 M compared to the nanosphere particles which could show an LOD of 0.5 × 10−9 M.

Smartphone-assisted point-of-care testing of nucleic acids based on hybridization chain reaction, magnetic beads, and gold nanorods etching

Colorimetric biosensors are simple but effective tools that are gaining popularity due to their ability to provide low-cost, rapid, and accurate detection for viruses like the Novel coronavirus, Influenza A, and Dengue virus, especially in point-of-care testing (POCT) and visual detection. In this study, a smartphone-assisted nucleic acid POCT was built using hybridization chain reaction (HCR), magnetic beads (MBs), and oxidized 3,3′,5,5′-tetramethylbenzidine (TMB2+)-mediated etching of gold nanorods (GNRs). The application of HCR without enzyme isothermal characteristics and MBs with easy separation, can quickly amplify nucleic acid signal and remove other reaction components. The blue shift of longitudinal localized surface plasmon resonance (LSPR) based on GNRs showed significant differences in etching color for different concentrations of target nucleic acid, which convert the signal into a visually semi-quantitative colorimetric result, achieving quantitative analysis with the color recognition software built into smartphones. This strategy, which only takes 40 min to detect and is two-thirds less time than the PCR, was successfully applied for the detection of the Dengue target sequence with a detection limit of 1.25 nM and exhibited excellent specificity for distinguishing single-base mutations, indicating broad application prospects in clinical laboratory diagnosis and enriching the research of nucleic acid POCT.