Particle Plasmon Resonance Research Articles

Investigation of dependent scattering criterion for dispersed particulate medium: Effects of metal particle plasmon resonances and host medium absorption

Spectral radiative transfer between particles within dispersed particulate medium is prevalent across various fields, which may be influenced by the microscopic dependent scattering effect (DSE). However, independent scattering assumption (ISA) is only employed in the radiative transfer of most studies, which can lead to significant errors. Consequently, there is an urgent need to establish the more accurate and widely applicable dependent scattering criterion for determining whether the radiative transfer is independent or dependent scattering. However, the most existing criteria are only applicable under the assumption of optically soft particles with weak absorption. This limitation results in the criteria being valid only for certain types of particles, excluding nonmetal particles with highly complex refractive indices and metal particles with strongly absorption. Furthermore, the existing criteria also fail to consider the impact of host medium absorption (HMA) on the localized surface plasmon resonance (LSPR) of metal particles and the DSE between particles. It would represent another significant limitation. To address these above limitations, this paper develops a comprehensive and systematic dependent scattering criterion with considering the plasmon resonances for metal particle and host medium absorption. The multiple sphere T-matrix (MSTM) method, generalized Mie scattering, and Monte Carlo ray tracing (MCRT) method are further employed to calculate and compare the radiative properties across different scales. The extinction cross section is the most suitable contrast parameter in the dependent scattering criterion with the consideration of host medium absorption. Clearance-to-wavelength ratio c/λ is used to characterize dependent scattering criterion. Consequently, the dependent scattering criterion c/λ for nonmetal particles is 6. While the dependent scattering criterion c/λ for metal particles is 5.5.

Label-Free Biosensor Based on Particle Plasmon Resonance Coupled with Diffraction Grating Waveguide.

Particle plasmon resonance (PPR), or localized surface plasmon resonance (LSPR), utilizes intrinsic resonance in metal nanoparticles for sensor fabrication. While diffraction grating waveguides monitor bioaffinity adsorption with out-of-plane illumination, integrating them with PPR for biomolecular detection schemes remains underexplored. This study introduces a label-free biosensing platform integrating PPR with a diffraction grating waveguide. Gold nanoparticles are immobilized on a glass slide in contact with a sample, while a UV-assisted embossed diffraction grating is positioned opposite. The setup utilizes diffraction in reflection to detect changes in the environment's refractive index, indicating biomolecular binding at the gold nanoparticle surface. The positional shift of the diffracted beam, measured with varying refractive indices of sucrose solutions, shows a sensitivity of 0.97 mm/RIU at 8 cm from a position-sensitive detector, highlighting enhanced sensitivity due to PPR-diffraction coupling near the gold nanoparticle surface. Furthermore, the sensor achieved a resolution of 3.1 × 10-4 refractive index unit and a detection limit of 4.4 pM for detection of anti-DNP. The sensitivity of the diffracted spot was confirmed using finite element method (FEM) simulations in COMSOL Multiphysics. This study presents a significant advancement in biosensing technology, offering practical solutions for sensitive, rapid, and label-free biomolecule detection.

Noninvasive Prenatal Genetic Screening of Cell-Free Fetal DNA for Early Prediction of β-Thalassemia Using Fiber Optic Nanogold-Linked Sorbent Assay.

β-Thalassemia is a prevalent type of severe inherited chronic anemia, primarily identified in developing countries. The identification of single nucleotide polymorphisms (SNPs) plays a vital role in the early diagnosis of genetic diseases. Here, we reported the development of an amplification-free fiber optic nanogold-linked sorbent assay method using a fiber optic particle plasmon resonance (FOPPR) biosensor for rapid and ultrasensitive detection of SNPs. Herein, MutS protein was selected as the biorecognition capture probe and immobilized on the sensing region to capture the target mutant DNA, which was hybridized with a single-base mismatched single-stranded DNA labeled by a gold nanoparticle (AuNP). The AuNP acts as a signaling agent to be detected by the FOPPR biosensor when it is bound on the fiber core surface. The method effectively differentiates mismatched double-stranded DNA by MutS protein from perfectly matched/complementary dsDNA. It exhibits an impressively low detection limit for the detection of SNPs at approximately 10-16 M using low-cost sensor chips and devices. By determination of the ratio of mutant DNA to normal DNA in cell-free genomic DNA from blood samples, this method is promising for diagnosing β-thalassemia in fetuses without invasive testing techniques.

Competitive Assay for the Ultrasensitive Detection of Organophosphate Pesticides Based on a Fiber-Optic Particle Plasmon Resonance Biosensor and an Acetylcholinesterase Binding Peptide.

An acetylcholinesterase (AChE) binding-based biosensor was developed for the ultrasensitive detection of organophosphate (OP) pesticides. The biosensor integrates the technique based on fiber-optic particle plasmon resonance detection and a synthetic AChE binding peptide conjugated with gold nanoparticles on the optical fiber surface via an AChE competitive binding assay. The OP pesticides present in the solution hinder the binding of AChE to the peptide on the biosensor by competing for the binding sites present in AChE. The limit of detection obtained for parathion using this method was observed to be 0.66 ppt (2.3 pM). This method shows a wide linear dynamic range of 6 orders. Furthermore, the use of the AChE binding peptide in the biosensor can better discriminate OPs against carbamates by using only a single biosensor. The practical application of this method was tested using spiked samples, which yielded good recovery and reproducibility. The spiked sample required minimal pretreatment before analysis; hence, this biosensor may also be used in the field.

Apolipoprotein E genetic analysis in unamplified genomic DNA extracts by ligase reaction and fiber optic particle plasmon resonance biosensor

Apolipoprotein E (APOE) genotyping is important for assessing the risk of late-onset Alzheimer's disease. We developed a DNA amplification-free method to perform APOE genetic analysis based on the high sensitivity of fiber optic particle plasmon resonance (FOPPR) biosensor and the specificity of ligase reaction. The method employed the dual-functional gold-iron oxide core-satellite hybrid nanoparticles (HNPs), which was modified with a single-stranded DNA (ssDNA) probe-P1, and a ssDNA probe-P2 modified with biotin to form a nanoplasmonic detection probe. Ligation of a ssDNA target complementary to the P1–P2 pair results in a ligation product with the HNP at one end and the biotin group at the other end, which can be captured by a streptavidin-functionalized sensor fiber, leading to an increase of nanoplasmonic absorption with magnitude useful for APOE genotype determination. Using synthetic ssDNA targets as standards, we achieved limits of detection in the range of 16–38 fM and the sensor responses from the mimic homozygous samples were about two times of that from mimic heterozygous samples at the same ssDNA concentration. For proof-of-principle, three genomic samples extracted from blood were analyzed and the results favorably agree with that by DNA sequencing.

Trace Determination of Grouper Nervous Necrosis Virus in Contaminated Larvae and Pond Water Samples Using Label-Free Fiber Optic Nanoplasmonic Biosensor.

We developed a fast (<20 min), label-free fiber optic particle plasmon resonance (FOPPR) immunosensing method to detect nervous necrosis virus (NNV), which often infects high-value economic aquatic species, such as grouper. Using spiked NNV particles in a phosphate buffer as samples, the standard calibration curve obtained was linear (R2 = 0.99) and the limit of detection (LOD) achieved was 2.75 × 104 TCID50/mL, which is superior to that obtained using enzyme-linked immunosorbent assay (ELISA). By using an enhancement method called fiber optic nanogold-linked immunosorbent assay (FONLISA), the LOD can be further improved to <1 TCID50/mL, which is comparable to that found by the conventional qPCR method. Employing the larvae homogenate samples of NNV-infected grouper, the results obtained by the FOPPR biosensor agree with those obtained by the quantitative polymerase chain reaction (qPCR) method. We also examined pond water samples from an infected container in an indoor aquaculture facility. The lowest detectable level of NNV coat protein was found to be 0.17 μg/mL, which is one order lower than the LOD reported by ELISA. Therefore, we demonstrated the potential of the FOPPR biosensor as an outbreak surveillance tool, which is able to give warning indication even when the trend of larvae death toll increment is still not clear.

Integration of Power-Free and Self-Contained Microfluidic Chip with Fiber Optic Particle Plasmon Resonance Aptasensor for Rapid Detection of SARS-CoV-2 Nucleocapsid Protein.

The global pandemic of COVID-19 has created an unrivalled need for sensitive and rapid point-of-care testing (POCT) methods for the detection of infectious viruses. For the novel coronavirus SARS-CoV-2, the nucleocapsid protein (N-protein) is one of the most abundant structural proteins of the virus and it serves as a useful diagnostic marker for detection. Herein, we report a fiber optic particle plasmon resonance (FOPPR) biosensor which employed a single-stranded DNA (ssDNA) aptamer as the recognition element to detect the SARS-CoV-2 N-protein in 15 min with a limit of detection (LOD) of 2.8 nM, meeting the acceptable LOD of 106 copies/mL set by the WHO target product profile. The sensor chip is a microfluidic chip based on the balance between the gravitational potential and the capillary force to control fluid loading, thus enabling the power-free auto-flowing function. It also has a risk-free self-contained design to avoid the risk of the virus leaking into the environment. These findings demonstrate the potential for designing a low-cost and robust POCT device towards rapid antigen detection for early screening of SARS-CoV-2 and its related mutants.

High Sensitivity Coreless Fiber Surface Plasmon Resonance Sensor Based on Au Nano Biconical Particles

A coupling enhanced surface plasmon resonance (SPR) sensor based on coreless fiber is proposed. Compared with the common fiber, the coreless fiber is easier to perceive the changes of the external medium environment. As one-dimensional material with superior performance, the Au nano biconical particles are used to improve the sensor performance. Based on the finite element method (FEM), the electric field enhancement effect of the coupling between the SPR of the gold film and the Localized surface plasmon resonance (LSPR) of the Au nano biconical particles on the surface of the coreless fiber is analyzed, and the experimental results show that the Au nano biconical particles can improve the sensitivity. The sensitivity of the improved Au nano biconical particle sensor is 3514 nm/RIU, which is 64% higher than that of the traditional gold film SPR sensor, and the quality factor is increased by 24%. The new sensor based on Au nano biconical particles and gold film has a good application prospect in biosensor and chemical measurement.

Single-particle spectroscopic investigation on the scattering spectrum of Au@MoS2 core-shell nanosphere heterostructure.

Owing to the uniform shape of the nanospheres, the Au@MoS2 core-shell nanosphere heterostructure enables us to design nano-optoelectronic devices and nanosensors with highly tunable and reproducible optical properties. However, until now, at the single-particle level, there is still uncertainty as to how much the scattering characteristics depend on the particle size and the local environment. In this letter, we performed an in situ single-particle study of the scattering spectrum of the Au@MoS2 core-shell nanosphere heterostructure before and after coating with the MoS2 layer. Single-particle characterization confirms that the classic quasi-static approximation (QSA) theory can be used to predict the scattering spectra of Au@MoS2 core-shell nanoparticles. Moreover, we have found that the A and B-exciton absorption peaks do not rely on the local refractive index change, while the position of the particle plasmon resonances does. Such features can be used as an internal reference for sensing applications against measurement errors, such as defocusing the imaging. Our results show that Au@MoS2 core-shell nanoparticles have the potential to become one of the promising nanosensors in the field of single-particle sensing.

Slab waveguide-based particle plasmon resonance optofluidic biosensor for rapid and label-free detection.

An effective bio-sensing platform that would meet the criteria of rapid, simple, and sensitive detection is crucial to translate bench research to clinical applications. However, simultaneously rapid and sensitive biosensing remains challenging for practical biomedical applications. In this study, for the first time, we demonstrate a cost-effective, label-free, real-time, and sensitive slab waveguide-based particle plasmon resonance (WGPPR) biosensor for practical clinical applications. A suspended glass slab waveguide structure with excellent optical confinement properties was designed and fabricated as the biosensor. Gold nanoparticles (AuNPs) were deposited on the top surface of the waveguide layer to significantly enhance the optical near field through the localized surface plasmon resonance (LSPR) effect. When light travels through the waveguide, the change in the local refractive index (RI) near the surface of the AuNPs can be transformed into changes in the intensity of transmitted light, thereby enabling sensitive and real-time detection. The RI sensing experiment shows a good sensor resolution of 1.43 × 10-4 RIU, which represents a 395% enhancement compared to that of the sensor without AuNPs. Through biochemical detection experiments, we measured IgG and determined the detection limit (LOD) at 614 ng mL-1 in ∼4 min, thereby proving the feasibility of the bio-detection sensing functionality. This study demonstrates a new type of WGPPR biosensor, which offers several unique advantages such as simple structure, high sensitivity, and rapid bio-sensing for practical bio-medical sensing applications. The new biosensor also fulfils point-of-care (POC) requirements.

Bioreduction (Ag+ to Ag0) and stabilization of silver nanocatalyst using hyaluronate biopolymer for azo-contaminated wastewater treatment

A facile and well-known eco-friendly strategy has been used to synthesize colloidal silver nanoparticles (AgNPs) and applied for the catalytic reduction of azo dyes. Herein, AgNPs were produced using silver nitrate (AgNO3) as a metal precursor and sodium hyaluronate (SH) as both reducing and stabilizing agents without the assistance of any other toxic reagents. The different characterizations were employed to investigate the morphology, crystallinity, surface plasmon resonance (SPR), particle size/distributions, and composition of particles. The investigation revealed that the AgNPs were mostly spherical/oval shape with an average size of 13.3 ± 4.7 nm, highly crystalline with a d-spacing of 0.233 – 0.257 nm, and coated with SH-macromolecules layer of cladding. In application of wastewater treatment, the AgNPs showed an excellent catalytic reduction (more than 99% rate of degradation) of two carcinogenic pollutants, i.e., reactive red 195 (RR195) and reactive yellow 145 (RY145) azo-dyes, with the support of sodium borohydride. The azo-dye catalysis has followed the model of pseudo-first-order kinetics reactions, with a kinetic constant (k) of 0.0948 min−1 (r2 = 0.9889) and 0.0222 min−1 (r2 = 0.9877) for RR195 and RY145, respectively. The present study not only provides a facile synthesis of AgNPs without toxic chemicals but also can be a potential candidate to meet the actual demand for textile wastewater treatment.

Synergistic effects of Ag inclusion in titania on its photocatalytic activity for the removal of methyl orange

Uniformly distributed Ag nanoparticles are successfully loaded on TiO2 nanoparticles with different Ag concentration through hydrothermal method. X-ray diffraction pattern and Raman spectra demonstrate the anatase phase of both TiO2 and Ag/TiO2. Loading of Ag on the surface of TiO2 shifts the wavelength of absorption edge to visible light resulting the narrow energy band gap. The photoluminescence intensity decreases with an increase in the concentration of Ag revealing a decrease in the recombination of electron-hole pairs. In order to test them in the photocatalysis, the degradation of textile dye methyl orange is used as a standard. Ag loaded TiO2 shows better photocatalytic performance than pure TiO2 because the higher surface area of the nanoparticles enabled them to function as good electron acceptors, delayed the electron-hole pair recombination and surface plasmon resonance of the silver particles. Moreover, 0.1 M of Ag/TiO2 nanoparticles (AT3) showed higher photocatalytic efficiency of 98.40% within 240 min light irradiation. The superior photocatalytic activity of Ag/TiO2 is attributed to the interactive effect caused by smaller crystallite size, narrow band gap, large surface area, and also enhancement in the charge separation.

Detection of Hg(II) at Part-Per-Quadrillion Levels by Fiber Optic Plasmonic Absorption Using DNA Hairpin and DNA-Gold Nanoparticle Conjugates

Mercury ion (Hg2+) is extremely toxic even at very low concentrations and its detection mainly relies on bulky and high-cost analytical instruments. Here, we introduce a fast and ultrasensitive biosensing method developed by the integration of fiber optic particle plasmon resonance and a highly selective molecular beacon with a stem-loop DNA structure immobilized on the unclad surface of an optical fiber. In the presence of Hg2+ ions and a free assisting DNA probe, the stem-loop opens and forms thymine–Hg2+–thymine complexes. A DNA reporting probe conjugated to gold nanoparticles is used as a label to interrogate the recognition event by binding with the terminal DNA binding domain of the opened stem-loop. The method provides a wide linear range of at least 5 orders from 10–14 to 10–9 M and an extremely low detection limit of 4.37 fM (0.876 ppq). It takes less than 15 min to analyze the concentration of Hg2+ ions in aqueous samples. The method is desirable for point-of-use applications because of its low-cost instrumentation and sensor chips, easy operation, and portability.

Excellent surface enhanced Raman properties of titanate nanotube-dopamine-Ag triad through efficient substrate design and LSPR matching

In this work, a novel triad nanocomposites containing trititanate nanotubes, Ag nanoparticles and dopamine were prepared and the SERS properties were measured experimentally. Control over the size and position of the Ag nanoparticles in the TiNT-dop-Ag system, along with the localised surface plasmon resonance (LSPR) of the Ag particles matching the Raman excitation wavelength, gives a SERS enhancement greater than 6 orders of magnitude. Electromagnetic modelling was used to provide a theoretical basis for these results.

Surface Lattice Resonances in Self‐Templated Plasmonic Honeycomb and Moiré Lattices

AbstractSurface lattice resonances appear in periodic plasmonic nanoparticle arrays due to the hybridization of plasmonic and photonic modes. Compared to localized surface plasmon resonances of single particles, these coupled modes feature reduced linewidth, angle‐dependent dispersion, and long‐range collectivity. Here, the optical response of self‐assembled plasmonic monolayers of periodically arranged gold and silver nanoparticles is studied. In comparison to already established hexagonal lattices, self‐templated honeycomb and Moiré type lattices as well as their binary counterparts that include silver and gold nanoparticles in the same monolayer are looked at. All periodic arrays feature macroscopic dimensions (cm‐scale) and support surface lattice resonances as evidenced from classical extinction measurements. The experimental findings are supported by results from finite difference time domain simulations. Variation of the plasmonic material, the lattice spacing, and geometry enables spectral tunability of the optical response of the lattices.

MutS protein-based fiber optic particle plasmon resonance biosensor for detecting single nucleotide polymorphisms.

A new biosensing method is presented to detect gene mutation by integrating the MutS protein from bacteria with a fiber optic particle plasmon resonance (FOPPR) sensing system. In this method, the MutS protein is conjugated with gold nanoparticles (AuNPs) deposited on an optical fiber core surface. The target double-stranded DNA containing an A and C mismatched base pair in a sample can be captured by the MutS protein, causing increased absorption of green light launching into the fiber and hence a decrease in transmitted light intensity through the fiber. As the signal change is enhanced through consecutive total internal reflections along the fiber, the limit of detection for an AC mismatch heteroduplex DNA can be as low as 0.49nM. Because a microfluidic chip is used to contain the optical fiber, the narrow channel width allows an analysis time as short as 15min. Furthermore, the label-free and real-time nature of the FOPPR sensing system enables determination of binding affinity and kinetics between MutS and single-base mismatched DNA. The method has been validated using a heterozygous PCR sample from a patient to determine the allelic fraction. The obtained allelic fraction of 0.474 reasonably agrees with the expected allelic fraction of 0.5. Therefore, the MutS-functionalized FOPPR sensor may potentially provide a convenient quantitative tool to detect single nucleotide polymorphisms in biological samples with a short analysis time at the point-of-care sites.

Integrated Graphene Oxide with Noble Metal Nanoparticles to Develop High-Sensitivity Fiber Optic Particle Plasmon Resonance (FOPPR) Biosensor for Biomolecules Determination

In this research, a direct, simple and ultrasensitive fiber optic particle plasmon resonance (FOPPR) biosensing platform for immunoglobulin G (IgG) detection was developed using a gold nanoparticle/graphene oxide (AuNP/GO) composite as signal amplification element. To obtain the best analytical performance of the sensor, experimental parameters including the surface concentration of GO on the AuNPs, formation time of the GO, the concentration of the anti-IgG and incubation time of anti-IgG were optimized. The calibration plots displayed a good linear relationship between the sensor response (ΔI/I0) and the logarithm of the analyte concentrations over a linear range from 1.0 × 10−10 to 1.0 × 10−6 g/mL of IgG under the optimum conditions. A limit of detection (LOD) of 0.038 ng/mL for IgG was calculated from the standard calibration curve. The plot has a linear relationship (correlation coefficient, R = 0.9990). The analytical performance of present work’s biosensor was better than that of our previously reported mixed self-assembled monolayer of 11-mercaptoundecanoic acid/6-mercapto-1-hexanol (MUA/MCH = 1:4) method by about three orders of magnitude. The achieved good sensitivity may be attributed to the synergistic effect between GO and AuNPs in this study. In addition, GO could immobilize more antibodies due to the abundant carboxylic groups on its surface. Furthermore, we also demonstrated that the results from this sensor have good reproducibility, with coefficients of variation (CVs) < 8% for IgG. Therefore, the present strategy provides a novel and convenient method for chemical and biochemical quantification and determination.

The applications of plasmonics biosensor and bamboo char filtration to the prevention of nervous necrosis virus infection in grouper farming ponds

Fiber optic particle plasmon resonance (FOPPR) biosensors have been useful tools to determine a variety of biological samples including viruses with superior detection limits than using conventional ELISA methods. In addition, without using tedious procedures required in ELISA protocols, FOPPR method can minimize contamination interferences and obtain accurate results in timely fashion. FOPPR biosensor is potentially a suitable virus detection device to implement in fish farms. In Taiwan, aquaculture products such as groupers suffer tremendous loss because of ineffective disease prevention efforts. The infected signs are not detected in the early stage before severe outbreak to cause uncontrollable consequences. Therefore when the virus level is low, using highly sensitive FOPPR biosensors to monitor pond water is a promising means to improve the effectiveness of aquatic product disease prevention by taking water treatment actions. We have also developed FOPPR assays to determine nervous necrosis virus (NNV), which cause massively high mortality rate (∼90%) in larva and juvenile stages of grouper species. Using coat proteins of NNV as standards in 2% salt water, the detection limit of 100 ng/mL is obtained. This limit is nearly 2 orders of magnitude lower than that using ELISA assays and adequate to indicate the severance level of NNV outbreak. Ground meat of infected juvenile grouper was diluted with saline to prepare simulated water samples. Ultra-low virus level of 40k TCID50 per mL is found in filtrate. The comparison determination data between using FOPPR and quantitative PCR methods are acceptable too. Unlike RT-PCR method not able to detect NNV RNA in pond water until severe infection, we demonstrate that FOPPR assay can detect NNV in pond water at very low NNV level at early infection stage, a couple of days prior to the outbreak occurrence. We also show that commercial FOPPR biosensor maintains stable immuno-sensing signal readout in indoor aquaculture settings. We will also discuss the potential applications of using FOPPR to monitor grouper larvae pond water to activate biochar filtration equipment when infection sign occurs.

Poles, physical bounds, and optimal materials predicted with approximated Mie coefficients

Resonant electromagnetic scattering with particles is a fundamental problem in electromagnetism that has been thoroughly investigated through the excitation of localized surface plasmon resonances (LSPR) in metallic particles or Mie resonances in high refractive index dielectrics. The interaction strength between electromagnetic waves and scatterers is limited by maximum and minimum physical bounds. Predicting the material composition of a scatterer that will maximize or minimize this interaction is an important objective, but its analytical treatment is challenged by the complexity of the functions appearing in the multipolar Mie theory. Here, we combine different kinds of expansions adapted to the different functions appearing in Mie scattering coefficients to derive simple and accurate expressions of the scattering electric and magnetic Mie coefficients in the form of rational functions. We demonstrate the accuracy of these expressions for metallic and dielectric homogeneous particles before deriving the analytical expressions of the complex eigen-frequencies (poles) for both cases. Approximate Mie coefficients can be used to derive simple but accurate expressions for determining complex dielectric permittivities that lead to poles of the dipolar Mie coefficient and ideal absorption conditions. The same expressions also predict the real dielectric permittivities that maximize (unitary limit) or minimize (anapole) electromagnetic scattering.

Dual-functional gold-iron oxide core-satellite hybrid nanoparticles for sensitivity enhancement in biosensors via nanoplasmonic and preconcentration effects.

A common strategy to improve the sensitivity of a biosensor for the detection of a low abundance analyte is to preconcentrate the analyte molecules before detection. A dual-functional gold-iron oxide core-satellite hybrid nanoparticle structure is proposed in this work to overcome the drawbacks of traditional sample pretreatment methods and the methods using non-magnetic nanomaterials for sample pretreatment. The new dual-functional hybrid nanoparticle structure can simultaneously serve as a signal reporter of a biorecognition event and a preconcentrator of a target at an extremely low concentration in a nanoplasmonic biosensor. By utilizing a fiber optic nanogold-linked sorbent assay in the fiber optic particle plasmon resonance (FOPPR) biosensor and an arbitrary DNA sequence as a target, we have demonstrated that the use of the new hybrid nanoparticle structure with magnetic preconcentration improves the limit of detection (LOD) for the DNA by 18 times as compared to the same method without magnetic preconcentration, so that the LOD for detecting the DNA can be as low as 2.6 fM. The new hybrid nanoparticle structure is easy to prepare and its use in the high-sensitivity and low-cost FOPPR biosensor provides vast opportunities in point-of-care applications.