Surface Plasmon Resonance Angle Shift Research Articles

Evaluation of PVC@Silver Nanocomposite as Sensor for Low Limit Detection of Cadmium Ion By Surface Plasmon Resonance Based Method

AbstractThis study explores the development of a PVC@Silver nanocomposite for enhanced detection of cadmium ions in water samples. Various characterization techniques confirmed the successful incorporation of silver nanoparticles into the polyvinyl chloride (PVC) matrix across different concentrations (1–4%). X-ray diffraction revealed the face-centered cubic crystalline structure of the silver nanoparticles, with the intensities of the (111), (200), (220), and (311) peaks increasing with higher Ag concentrations. The average crystallite sizes ranged from 26.1 nm (3% Ag) to 30.0 nm (2% Ag). Dynamic light scattering showed nanoparticle sizes of 24–43 nm, while zeta potential values of -24 to -40 mV indicated reasonable colloidal stability. Brunauer–Emmett–Teller (BET) surface area analysis demonstrated a decreasing surface area from 30.09 m2/g (1% Ag) to 25.27 m2/g (3% Ag), attributed to pore filling by silver nanostructures. Significantly, the PVC@Silver nanocomposite facilitated sensitive detection of Cd(II) ions using surface plasmon resonance (SPR), exhibiting an SPR angle shift of 26.30° with intensity values ranging from 10.80 (4% Ag) to 12.19 (3% Ag). UV–vis spectra revealed a prominent surface plasmon resonance band at 420–430 nm, indicating the presence of silver nanoparticles. The optical band gap varied from 4.51eV (1% Ag) to 4.12eV (4% Ag).

Genetically encoded phosphatidylserine biosensor for in vitro, ex vivo and in vivo labelling

BackgroundThe dynamics of phosphatidylserine in the plasma membrane is a tightly regulated feature of eukaryotic cells. Phosphatidylserine (PS) is found preferentially in the inner leaflet of the plasma membrane. Disruption of this asymmetry leads to the exposure of phosphatidylserine on the cell surface and is associated with cell death, synaptic pruning, blood clotting and other cellular processes. Due to the role of phosphatidylserine in widespread cellular functions, an efficient phosphatidylserine probe is needed to study them. Currently, a few different phosphatidylserine labelling tools are available; however, these labels have unfavourable signal-to-noise ratios and are difficult to use in tissues due to limited permeability. Their application in living tissue requires injection procedures that damage the tissue and release damage-associated molecular patterns, which in turn stimulates phosphatidylserine exposure.MethodsFor this reason, we developed a novel genetically encoded phosphatidylserine probe based on the C2 domain of the lactadherin (MFG-E8) protein, suitable for labelling exposed phosphatidylserine in various research models. We tested the C2 probe specificity to phosphatidylserine on hybrid bilayer lipid membranes by observing surface plasmon resonance angle shift. Then, we analysed purified fused C2 proteins on different cell culture lines or engineered AAVs encoding C2 probes on tissue cultures after apoptosis induction. For in vivo experiments, neurotropic AAVs were intravenously injected into perinatal mice, and after 2 weeks, brain slices were collected to observe C2-SNAP expression.ResultsThe biophysical analysis revealed the high specificity of the C2 probe for phosphatidylserine. The fused recombinant C2 proteins were suitable for labelling phosphatidylserine on the surface of apoptotic cells in various cell lines. We engineered AAVs and validated them in organotypic brain tissue cultures for non-invasive delivery of the genetically encoded C2 probe and showed that these probes were expressed in the brain in vivo after intravenous AAV delivery to mice.ConclusionsWe have demonstrated that the developed genetically encoded PS biosensor can be utilised in a variety of assays as a two-component system of C2 and C2m2 fusion proteins. This system allows for precise quantification and PS visualisation at directly specified threshold levels, enabling the evaluation of PS exposure in both physiological and cell death processes.

Green Synthesis of Fe3O4/Chitosan Nanoparticles Utilizing Moringa Oleifera Extracts and Their Surface Plasmon Resonance Properties

In this study, a simple, rapid, and environmentally friendly green approach for synthesizing Fe3O4 and Fe3O4/chitosan nanoparticles with various concentrations was developed. The nanoparticles had a spherical shape with a cubic inverse spinel structure. The functionalization of the Fe3O4 nanoparticles using chitosan increased the crystallite size of the nanoparticles from 7.2 to 7.8 nm. The Fourier transform infrared spectra of the Fe3O4/chitosan nanoparticles showed the existence of the characteristic peaks of chitosan in addition to a peak at 578 cm−1, which corresponds to the stretching of the Fe−O group. The UV-visible spectra demonstrated a wide absorption band with the appearance of small peaks of chitosan absorption at 205 and 215 nm. The saturation magnetization of the Fe3O4 was 54.1 emu g−1. The surface plasmon resonance (SPR) measurements showed an enhancement in the SPR angle as the ratio of chitosan to Fe3O4 increased, wherein the angle shift from 0.17° to 1.91°. The chitosan covering the Fe3O4 nanoparticle surface caused the refractive index to change, which increased the SPR angle shift. The obtained results indicated that the SPR properties of the Fe3O4 nanoparticles were significantly improved by modification with chitosan. These results also indicated that the use of chitosan in Fe3O4 nanoparticles can enhance SPR properties, which has potential for future SPR-based sensor applications.

Effect of Temperature on the Surface Plasmon Resonance (SPR) Mode along a Metal - Liquid Crystal Interface

The effect of temperature on the surface plasmon mode parameters for surface plasmons (SPs) excited by prism coupling along the interface of a thin silver film and homeotropically aligned liquid crystals (LCs), 5CB and UCF25 are theoretically studied. The change in the SPR angle of dip with temperature is found to be almost linear below the clearing temperature of the LCs. The temperature sensitivity is found to be high in the temperature range where the LC behaves as an anisotropic material. The sensitivity is found to be higher when SPR reflectance at a fixed incident angle is used as the variable parameter. The shift in SPR angle of dip is found to be linear with the change in birefringence of the LC due to the change in temperature. The change in SPR parameters with temperature is found to be much lesser in the temperature range where the LC behaves as an isotropic material.

Continuous Detection of Pb(II) utilizing Chitosan-Graphene Oxide Surface Plasmon Resonance Sensors based on Ag/Au and Au/Ag/Au Nanolayers

This work demonstrates the effect of Ag/Au and Au/Ag/Au nanolayers on the performance of chitosan (CS)-graphene oxide (GO) surface plasmon resonance (SPR) sensors for Pb(II) ion detection. The CS-GO SPR sensors are fabricated on a bi-metallic 40 nm Ag/10 nm Au and tri-metallic 10 nm Au/40 nm Ag/10 nm Au nanolayers. The sensors are tested with Pb(II) ion solution of concentrations 0.1 to 5 ppm using SPR spectroscopy. The results show that the CS-GO SPR sensor on the bimetallic Ag/Au gives a gradual shift in SPR angle from 0.1 to 1 ppm and slightly linear from 3 to 5 ppm. Meanwhile, the CS-GO SPR sensor on the tri-metallic Au/Ag/Au nanolayers provides an extended linearity range from 1 to 5 ppm with the highest shift in SPR angle of 1.8o. Additionally, the tri-metallic CS-GO SPR sensor also exhibits the greatest SNR of 0.25 as compared to 0.15 of the one on the bi-metallic nanolayers. Thus, the studies prove that the tri-metallic Au/Ag/Au nanolayer is an effective and simple approach to improve the performance of a CS-GO SPR sensor for Pb(II) ion detection.

Magnetic field-aligned Fe3O4-coated silver magnetoplasmonic nanochain with enhanced sensitivity for detection of Siglec-15

Noble metal nanoparticles could provide a significant gain in sensitivity of surface plasmon resonance (SPR) sensor by electromagnetic field coupling between the localized plasmon resonance of nanoparticles and gold film. A facile and cost-effective SPR sensor based on magnetic field-aligned Fe3O4-coated silver magnetoplasmonic nanoparticles (Ag@MNPs) nanochain (M-Ag@MNPs) was proposed to improve the sensitivity of the sensor, which gave access to detect clinical targets at low concentration. Optimization experiments proved that 80 ng mL−1 M-Ag@MNPs-based SPR sensor showed high refractive index sensitivity and increased detection accuracy and quality factor when comparing with those of bare gold. Sialic acid binding Ig like lectins-15 (Siglec-15) was used as proof of concept to verify the sensitivity enhancement performance of M-Ag@MNPs in the actual detection process. SPR angle shifts of M-Ag@MNPs/gold sensor were significantly higher than those of traditional gold sensor under the same concentration of Siglec-15, which was consistent with previous performance analysis. Also, the detection limit of M-Ag@MNPs/gold sensor was calculated to be 1.36 pg mL−1. All these results had proved that aligning M-Ag@MNPs onto the gold chip could improve the performance of the SPR sensor and achieve sensitive detection of small amounts of clinical biomarkers.

The effect of the concentration of the stabilizer in the formation of a silver nanoparticle on the phenomenon of Surface Plasmon Resonance (SPR) as an active material for biosensor

It has been successfully synthesized silver nanoparticles by chemical reduction methods. Silver nitrate (AgNO3) is used as a metal precursor and trisodium citrate as a reducing agent with varying concentrations of the stabilizer PVA. The UV-Vis spectrometer shows that increasing the mass concentration of the stabilizer can sharpen the surface plasmon maximum absorption band and there is a shift in the maximum absorption band towards a larger wavelength. This shift occurred from a wavelength of 428.79 nm at a PVA concentration of 0.85 ppm shifted to a wavelength of 429.01 nm, 430.93 nm and 434.13 nm for each PVA concentration of 1.70 ppm, 2.55 ppm and 4.25 ppm. The observation results of the SPR phenomenon showed a shift in the SPR angle when a thin layer of silver as the active ingredient of the sensor was coated with silver nanoparticles. This addition also sharpens the reflectance value. The SPR angle shift and the increase in reflectance value are caused by changes in the surface plasmon wave constant, which becomes a reference that the SPR phenomenon by modifying the sensing surface using an additional layer of silver nanoparticles can increase its sensitivity.

Clinical Application for Screening Down's Syndrome by Using Carboxylated Graphene Oxide-Based Surface Plasmon Resonance Aptasensors.

BackgroundAdvanced medical detection technology requires high sensitivity and accuracy to increase the disease detection rate. We showed that carboxyl-functionalized graphene oxide (carboxyl-GO) biosensing materials are capable of accurate detection.MethodsWe developed a carboxylated GO-based surface plasmon resonance (SPR) aptasensor suitable for screening Down’s syndrome in clinical serum. This biosensing material could rapidly and accurately detect hCG protein with a low concentration to identify fetal Down’s syndrome. The developed carboxyl-GO-based SPR aptasensor showed excellent sensitivity and limit of detection without the use of antibodies and without any specific preference.ResultshCG protein detection limits of 1 pM in buffer samples and 1.9 pM in clinical serum samples were achieved. The results showed that the carboxyl-GO-based chip could detect hCG well below the normal physiological level of serum protein (5.0 mIU/mL). High affinity, sensitivity, and better detection limit were obtained in the range of 1.9 pM to 135 pM. The results showed a 5k-fold dilution factor, and that an SPR angle shift of more than 20 millidegrees (mo) was associated with a significant risk of fetal Down’s syndrome compared to normal pregnant women. The results clearly showed that the detection of hCG protein in serum samples from pregnant women at 12–19 weeks could be used to screen Down’s syndrome with high selectivity and sensitivity.ConclusionOur findings suggest the potential application of carboxyl-GO film in proof-of-concept studies for serum assays as a new type of SPR material. In addition, peptide and carboxyl-GO films may be conducive to the development of future point of care testing and rapid diagnostic devices for other diseases such as cancer.

Label-free Binding Analysis of 4-(2-Pyridylazo)-resorcinol-based Composite Layer with Cobalt Ion Using Surface Plasmon Resonance Optical Sensor

Label-free measurements of small-molecule binding interactions are of high interest to researchers across multiple scientific disciplines. Label-free optical sensors based on surface plasmon resonance (SPR) have been widely used for detecting various targets including toxic heavy metals in solutions. In this research, an SPR optical sensor enhanced with a 4-(2-pyridylazo)-resorcinol (PAR)-based composite layer was employed for the detection of the cobalt ion (Co2+). A binding analysis study was conducted by monitoring the interaction between Co2+ and the sensing layer thin film. In our experiment, there were no changes in SPR angle for a gold layer in contact with Co2+ of different concentrations, whereas the enhanced SPR sensor produced a maximum SPR angle shift of 0.328°. From the relationship between the angle shift and the concentration of Co2+, the sensor had a sensitivity of 0.2375° ppm−1 for concentrations of less than 1 ppm, 0.0044° ppm−1 for concentrations of 1 to 10 ppm, and 0.00069° ppm−1 for concentrations from 10 to 100 ppm. Further analysis was also carried out by calculating the full width at half maximum (FWHM), detection accuracy (DA), and signal-to-noise ratio (SNR). In the binding analysis, the experimental results were fitted with Langmuir, Freundlich, and Sips isotherm equations. It was found that the Sips isotherm equation most closely fitted the experimental data with an R2 value of 0.96716 and a binding affinity of 1.649 ppm−1.

High-Sensitivity Detection of the Lung Cancer Biomarker CYFRA21-1 in Serum Samples Using a Carboxyl-MoS2 Functional Film for SPR-Based Immunosensors.

We constructed a novel surface plasmon resonance (SPR) detection assay using carboxyl-functionalized molybdenum disulfide (carboxyl-MoS2) nanocomposites as a signal amplification sensing film for the ultrasensitive detection of the lung cancer-associated biomarker cytokeratin 19 fragment (CYFRA21-1). The experiment succeeded in MoS2 reacted with chloroacetic acid giving carboxyl-MoS2 as the reaction product. The additional shoulder in the C 1s and O 1s peaks of carboxyl-MoS2, which were increased in X-ray photoelectron spectroscopy, confirmed the presence of O–C=O groups on the surface of the carboxyl-MoS2. Compared to MoS2, the experimental results confirmed that carboxyl-modified MoS2 had improved low impedance and low refractive index. The carboxyl-MoS2-based chip had a high affinity, with an SPR angle shift enhanced by 2.6-fold and affinity binding KA enhanced by 15-fold compared to a traditional SPR sensor. The results revealed that the carboxyl-MoS2-based chip had high sensitivity, specificity, and SPR signal affinity, while the CYFRA21-1 assay in spiked clinical serum showed a lower detection limit of 0.05 pg/mL and a wider quantitation range (0.05 pg/mL to 100 ng/mL). The carboxyl-MoS2-based chip detection value was about 104 times more sensitive than the limit of detection of an enzyme-linked immunosorbent assay (ELISA) (0.60 ng/mL). The results showed that the carboxyl-MoS2-based chip had the potential to rapidly assay complex samples including bodily fluids, whole blood, serum, plasma, urine, and saliva in SPR-based immunosensors to diagnose diseases including cancer.

Simultaneous Real-Time Detection of Pregnancy-Associated Plasma Protein-A and -A2 Using a Graphene Oxide-Based Surface Plasmon Resonance Biosensor.

BackgroundPregnancy-associated plasma protein-A and -A2 (PAPP-A and -A2) are principally expressed in placental trophoblasts and play a critical role in the regulation of fetal and placental growth. PAPP-A2 shares 45% amino acid similarity with PAPP-A. This study aimed to investigate the efficacy of real-time detection of PAPP-A and PAPP-A2 using a novel surface plasmon resonance (SPR) biosensor based on graphene oxide (GO).MethodsTraditional SPR and GO-based SPR chips were fabricated to measure PAPP-A and PAPP-A2 concentrations. We compared SPR response curves of PAPP-A and PAPP-A2 between traditional SPR and GO-SPR biosensors. We also performed interference tests and specificity analyses among PAPP-A, PAPP-A2, and mixed interference proteins.ResultsThe time to detect PAPP-A and PAPP-A2 was about 150 seconds with both traditional SPR and GO-SPR biosensors. Approximately double SPR angle shifts were noted with the GO-SPR biosensor compared to the traditional SPR biosensor at a PAPP-A and PAPP-A2 concentration of 5 μg/mL. The limit of detection of the GO-SPR biosensor was as low as 0.5 ng/mL for both PAPP-A and PAPP-A2. Interference testing revealed that almost all of the protein bonded on the GO-SPR biosensor with anti-PAPP-A from the mixture of proteins was PAPP-A, and that almost no other proteins were captured except for PAPP-A2. However, the SPR signal of PAPP-A2 (5.75 mdeg) was much smaller than that of PAPP-A (13.76 mdeg). Similar results were noted with anti-PAPP-A2, where almost all of the protein bonded on the GO-SPR biosensor was PAPP-A2. The SPR signal of PAPP-A (5.17 mdeg) was much smaller than that of PAPP-A2 (13.94 mdeg).ConclusionThe GO-SPR biosensor could distinguish PAPP-A and PAPP-A2 from various mixed interference proteins with high sensitivity and specificity. It could potentially be used to measure PAPP-A and PAPP-A2 in clinical blood samples during pregnancy.

Design and analysis of surface plasmon resonance optical sensor for determining cobalt ion based on chitosan-graphene oxide decorated quantum dots-modified gold active layer.

In this study, the incorporation of surface plasmon resonance (SPR) spectroscopy with novel chitosan-graphene oxide/cadmium sulphide quantum dots (CdS QDs) active layer for cobalt ion (Co2+) detection has been developed. The interaction of different Co2+ concentrations with the novel modified active layer was monitored using the SPR technique. From the SPR results, detection range, sensitivity, full width at half maximum (FWHM), detection accuracy (DA) and signal-to-noise ratio (SNR) have been analysed. The results showed the detection range of this optical sensor was 0.01 to 10 ppm, and it was saturated for higher concentration of Co2+. The sensitivity obtained was 0.1188 ppm-1 for low concentration of Co2+ ranged from 0.01 to 1 ppm. The FWHM and DA were consistent for all concentration of Co2+, while the SNR of the SPR signal increased with the Co2+ concentration. The SPR angle shifts were also fitted using Langmuir, Freundlich and Sips (Langmuir-Freundlich) isotherm models, where Sips model fitted the best with the binding affinity of 0.939 ppm-1. The results proved that the novel chitosan-graphene oxide/CdS QDs modified gold thin film can detect Co2+ via SPR spectroscopy.

The effect of variation of reducing agent concentration on optical properties of silver nanoparticles as active materials in surface plasmon resonance (SPR) biosensor

Using chemical reduction methods, silver nanoparticles have been successfully synthesized. As a precursor, silver nitrate (AgNO3) was used and as a reducing agent was trinatrium citrate. In the process of synthesis, there was a variation of concentration of the reducing agent of trinatrium citrate. Optical properties of silver nanoparticles formation and structure in a colloidal solution were studied by using a UV-Vis spectrometer. In this synthesis process, the colloid nanoparticles produced dominated by silver nanoparticle grains since the yellowish color formed in the sample. The UV-Vis spectrometer shows that there is a shift in the spectrum of silver nanoparticles colloidal absorption in the range of 429.01 nm to 433.06 nm for the variation of trinatrium citrate reducing agent concentration to the colloid formation of the silver nanoparticles. A shift in the angle of SPR is observed when a thin silver layer as the active material of the sensor is coated silver nanoparticles. Increasing the concentration of reducing substances of a thin silver nanoparticles films will shifts the angle of SPR. This SPR angle shift sharpens the reflectivity value and changes the surface plasmon wave constants due to changes in the surface plasmon constant which is caused by changes in the dielectric constant of thin silver nanoparticles films.

A Detailed Study on the Fabrication of Surface Plasmon Sensor Chips: Optimization of Dextran Molecular Weight

The present work discusses a detailed study of the fabrication steps of carboxymethyl-dextran SPR sensor chips with specal focus on the effect of dextran molecular weight (40, 200, and 500 kDa) both on the chip physical characteristics after each fabrication step and on toxin detection performance. Physical characterization was performed using ATR-FTIR, AFM, profilometry, and surface plasmon resonance (SPR) as analytical methods. Based on ATR-FTIR spectroscopy analysis, it is demonstrated that NaOH concentration plays a critical role in the epichlorohydrin (ECH) activation step for subsequent dextran molecules covalent bonding and should be less than 0.4 M, preferably 0.2 M. This is in contrast to the concentration of 0.4 M used in conventional protocols. After covalent binding of the monoclonal anti-staphylococcal enterotoxin B (anti-SEB) to the carboxyl groups of dextran matrix, the detection of enterotoxin B as a function of dextran molecular weight has been assessed. Dextran with a molecular weight of 200 kDa results in a distinct larger SPR angle shift of the final chip with respect to 40 and 500 kDa molecular weights. This observation is explained based on the SPR theory and the physico-chemical characteristics of the antibody/dextran layers measured throughout this study. The SPR sensor chip with the dextran molecular weight of 200 kDa may be considered as an appropriate candidate for the detection of proteins with the same molecular weight as enterotoxin B.

Label-free optical spectroscopy for characterizing binding properties of highly sensitive nanocrystalline cellulose-graphene oxide based nanocomposite towards nickel ion.

Surface plasmon resonance (SPR) is a label-free optical spectroscopy that is widely used for biomolecular interaction analysis. In this work, SPR was used to characterize the binding properties of highly sensitive nanocrystalline cellulose-graphene oxide based nanocomposite (CTA-NCC/GO) towards nickel ion. The formation of CTA-NCC/GO nanocomposite has been confirmed by FT-IR. The SPR analysis result shows that the CTA-NCC/GO has high binding affinity towards Ni2+ from 0.01 until 0.1 ppm with binding affinity constant of 1.620 × 103 M-1. The sensitivity for the CTA-NCC/GO calculated was 1.509° ppm-1. The full width at half maximum (FWHM), data accuracy (DA), and signal-to-noise ratio (SNR) have also been determined using the obtained SPR curve. For the FWHM, the value was 2.25° at 0.01 until 0.08 ppm and decreases to 2.12° at 0.1 until 10 ppm. The DA for the SPR curves is the highest at 0.01 until 0.08 ppm and lowest at 0.1 until 10 ppm. The SNR curves mirrors the curves of SPR angle shift where the SNR increases with the Ni2+ concentrations. For the selectivity test, the CTA-NCC/GO has the abilities to differentiate Ni2+ in the mixture of metal ions.

Development of an optical sensor based on surface plasmon resonance phenomenon for diagnosis of dengue virus E-protein

Application of surface plasmon resonance (SPR) optical sensor in the diagnosis of dengue virus (DENV) emerged over recent years. Immobilized monoclonal antibody (IgM) on gold/Fe-MPA-NCC-CTAB/EDC-NHS thin film was prepared using a spin coating technique. DENV E-protein can be detected by measuring the SPR signal when IgM immobilized gold/Fe-MPA-NCC-CTAB/EDC-NHS thin film is exposed to the DENV E-protein solution, by varying the concentration ranging from 0.0001 nM to 10 nM. A linear relationship between the shift of SPR angle and concentration of DENV E-protein up to 0.01 nM, with sensitivity of 39.96° nM−1 has been observed. The surface morphology of sensor chip was also recorded using atomic force microscopy to confirm the presence of bound DENV E-protein into IgM surface.

Surface Plasmon Resonance (SPR) Phenomenon of the Oxidizing and Reducing Polypyrrole

Surface Plasmon Resonance (SPR) phenomenon of the oxidizing and reducing polypyrrole (PPy) have been observed using a modified Au/PPy Kretschmann configuration. The observation was carried out through simulation Winspall 3.02 software and compared with some experimental data refractive index (n), absorbance index (), and thickness (τ) reported in other literatures with spectroscopy ellipsometry. This simulation assumed that the SPR system use BK-7 halfcylinder prism (n= 1,515) and the laser beam was generated by HeNe (λ= 632,8 nm). The result showed that the optimum layer thickness of polypyrrole with neutral electrolyte solution in the reduction state is of about 20 nm. The polypyrrole with an acid solution in the oxidation state showed that the reflectivity curve is sharper and the width of the curve is smaller than the neutral electrolyte solution in the reduction state with the SPR angle of about 46,810 and the reflectivity value of about 0,217. Polypyrrole in a state of oxidation and reduction, related to the absorption, film thickness, and dielectric constant of materials, affected to the SPR angle shift and dip curve

Monitoring Microalgae Population Growth by using Fe3O4 Nanoparticles-based Surface Plasmon Resonance (SPR) Biosensor

The population growth of microalgae has been successfully monitored by using the surface plasmon resonance (SPR)-based biosensor activated by using PEG-4000 functionalized Fe3O4 magnetic nanoparticles. The SPR-based biosensor in this work used Kretchmann configuration and Ha-Ne laser beam (λ = 633nm). The population of microalgae were estimated by using calibration curve. The shift of SPR angle happens due to the change of dielectric medium from prism/Au/air system to prism/Au/Fe3O4+PEG+microalgae/cover glass system. The change of dielectric medium occurs due to deposition of Fe3O4+PEG+microalgae samples that were monitored for seven days. The population of microalgae on the first day was estimated of 1188146 cell/ml and SPR angle had shifted from 42.80 to 69.00. The SPR angle shifted as much as 26.20. The population of microalga grew significantly on the third day as much as 1649106 cell/ml and the SPR angle had shifted 43.80 to 71.10. The SPR angle shifted as much as 27.30. On fourth to seventh day, the population of microalgae decreased. The population of microalgae on the seventh day was estimated of 1206961 cell/ml and the SPR angle had shifted from 44.00 to 68.80. The SPR angle shifted as much as 24.8 degrees. The shift of SPR angle was influenced by the population of microalgae so that the SPR-based biosensor has the potential for use in monitoring the microalgae population.

A Surface Plasmon Resonance Histamine Sensor Based on an Electropolymerized Molecularly Imprinted Polymer (E-MIP)

In this paper, histamine sensing by surface plasmon resonance (SPR) spectroscopy using an electropolymerized molecularly imprinted polymer (E-MIP) of functionalized polyterthiophene and histamine is reported. The MIP histamine sensor showed good linear relationship (R 2 = 0.995) between the SPR angle shift and the logarithm of histamine concentration, ranging from 15 – 500 μg/mL, with a limit of detection (LOD) of 2.0 μg/mL and a calibration sensitivity of 44.6 m° per log μg/mL histamine. Results also showed higher binding affinity of histamine for the MIP sensor than for the non-imprinted (NIP) sensor indicating excellent specificity. Moreover, the selectivity of the MIP histamine sensor against some of its structural analogues was demonstrated.

HRP-Mimicking DNAzyme-Catalyzed in Situ Generation of Polyaniline To Assist Signal Amplification for Ultrasensitive Surface Plasmon Resonance Biosensing

It is well-known that the horseradish peroxidase- (HRP-) mimicking DNAzyme, namely, hemin/G-quadruplex, can effectively catalyze the polymerization of aniline to form DNA-guided polyaniline. Meanwhile, polyaniline exhibits extraordinary electrical, electrochemical, and redox properties, as well as excellent SPR signal-enhancing ability. Herein, we report a novel ultrasensitive surface plasmon resonance (SPR) biosensor based on HRP-mimicking DNAzyme-catalyzed in situ formation of polyaniline for signal amplification, using bleomycin (BLM) as the proof-of-concept analyte. The recognition and the subsequent cleavage of DNA probe P1 by BLM switches off the hybridization between P1 and the G-rich DNA probe P2, resulting in less hemin/G-quadruplex complexes and reduced DNA-guided polyaniline deposition on the SPR Au disk surface. As compared to the case when BLM is absent, a significant shift in SPR angle is observed, which is dependent on the BLM concentration. Therefore, ultrasensitive SPR detection of the target BLM is realized, with a detection limit down to 0.35 pM, much lower than those reported in the literature. Moreover, the proposed SPR biosensor has been successfully applied for the detection of BLM spiked in human serum samples. The HRP-mimicking DNAzyme-catalyzed in situ polyaniline deposition and polyaniline-assisted signal amplification not only significantly improves the specificity and the sensitivity of the BLM assay but also allows the ultrasensitive detection of other biomolecules by simply changing the specific target recognition DNA sequences, thus providing a versatile SPR biosensing platform for the ultrasensitive detection of a variety of analytes and showing great potential for application in the fields of bioanalysis and clinical biomedicine.