Enhancing Sensitivity of Surface Plasmon Resonance Biosensors by Functionalized Gold Nanoparticles: Size Matters

Recent development of gold nanochips in biosensing and biodiagnosis sensibilization strategies in vitro based on SPR, SERS and FRET optical properties

Gold nanomaterials have become attractive nanomaterials for biomedical research due to their unique physical and chemical properties, and nanochips are designed to manufacture high-quality substrates for loading gold nanoparticles (GNPs) to achieve specific and selective detection. By utilizing multiple optical properties of different gold nanostructures, the sensitivity, specificity, speed, contrast, resolution, and other performance of biosensing and biological diagnosis can be significantly improved. This paper summarized the sensitivity enhancement strategies of optical biosensing techniques based on the three main optical properties of gold nanomaterials: surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and fluorescence resonance energy transfer (FRET). The aim is to comprehensively review the development direction of in vitro diagnostics (IVDs) from two aspects: detection strategies and modification of gold nanomaterials. In addition, some opportunities and challenges that gold-based IVDs may encounter at present or in the future are also mentioned in this paper. In summary, this paper can enlighten readers with feasible strategies for manufacturing potential gold-based nanobiosensors.

Electrochemical detection of poly(ADP-ribose) polymerase-1 with silver nanoparticles as signal labels by integrating the advantages of homogeneous reaction with surface-tethered detection

Poly(ADP-ribose)polymerase-1 (PARP1) could be activated by binding to nucleic acids with specific sequences, thus catalyzing the poly-ADP-ribosylation (PARylation) of target proteins including PARP1 itself. Most of the previously reported electrochemical methods for the determination of PARP1 were relied on the electrostatic interactions, which required the pre-immobilization of DNA on an electrode for the capture of PARP1. Herein, we reported an "immobilization-free" electrochemical strategy for the assays of PARP1 on the basic of avidin-biotin interaction. Once PARP1 was activated by binding with the specific double-stranded DNA (dsDNA) in a homogeneous solution, the biotinylated nicotinamide adenine dinucleotide (biotin-NAD+) was transferred onto PARP1, resulting in the formation of biotinylated PAR polymers. The resulting biotinylated PAR polymers were then captured by a neutravidin (NA)-modified electrode through avidin-biotin interactions. The rich biotin moieties in the PAR polymers allowed for the capture of NA-modified silver nanoparticles (NA-AgNPs) through the avidin-biotin interactions. The surface-tethered AgNPs produced a well-defined electrochemical signal due to the characteristic solid-state Ag/AgCl process. The "immobilization-free", electrostatic interaction-independent electrochemical biosensor exhibited low background current, high sensitivity, and good stability. It has achieved the determination of PARP1 with a detection limit down to 0.7 mU. The biosensor was further applied to determine the inhibition efficiency of potential inhibitors with a satisfactory result. This method shows promising potential applications in PARP1-related clinical diagnosis and drug discovery.

Lysozyme-sensitive plasmonic hydrogel nanocomposite for colorimetric dry-eye inflammation biosensing

Detection of lysozyme levels in ocular fluids is considered crucial for diagnosing and monitoring various health and eye conditions, including dry-eye syndrome. Hydrogel-based nanocomposites have been demonstrated to be one of the most promising platforms for fast and accurate sensing of different biomolecules. In this work, hydrogel, electrospun nanofibers, and plasmonic nanoparticles are combined to fabricate a sensitive and easy-to-use biosensor for lysozyme. Poly(L-lactide-co-caprolactone) (PLCL) nanofibers were covered with silver nanoplates (AgNPls), providing a stable plasmonic platform, where a poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogel layer allows mobility and good integration of the biomolecules. By integrating these components, the platform can also exhibit a colorimetric response to the concentration of lysozyme, allowing for easy and non-invasive monitoring. Quantitative biosensing operates on the principle of localized surface plasmon resonance (LSPR) induced by plasmonic nanoparticles. Chemical, structural, thermal, and optical characterizations were performed on each platform layer, and the platform's ability to detect lysozyme at concentrations relevant to those found in tears of patients with dry-eye syndrome and other related diseases was investigated by colorimetry and UV-Vis spectroscopy. This biosensor's sensitivity and rapid response time, alongside the easy detection by the naked eye, make it a promising tool for early diagnosis and treatment monitoring of eye diseases.

Functionalized gold nanoparticle enhanced nanorod hyperbolic metamaterial biosensor for highly sensitive detection of carcinoembryonic antigen

Hyperbolic metamaterial (HMM) biosensors based on metals have superior performance in comparison with conventional plasmonic biosensors in the detection of low concentrations of molecules. In this study, a nanorod HMM (NHMM) biosensor based on refractive index changes for carcinoembryonic antigen (CEA) detection is developed using secondary antibody modified gold nanoparticle (AuNP-Ab2) nanocomposites as signal amplification element for the first time. Numerical analysis based on finite element method is conducted to simulate the perturbation of the electric field of bulk plasmon polariton (BPP) supported by a NHMM in the presence of a AuNP. The simulation reveals an enhancement of the localized electric field, which arises from the resonant coupling of BPP to the localized surface plasmon resonance supported by AuNPs and is beneficial for the detection of changes of the refractive index. Furthermore, the AuNP-Ab2 nanocomposites-based NHMM (AuNP/Ab2-NHMM) biosensor enables CEA detection in the visible and near-infrared regions simultaneously. The highly sensitive detection of CEA with a wide linear range of 1-500 ng/mL is achieved in the near-infrared region. The detectable concentration of the AuNP/Ab2-NHMM biosensor has a 50-fold decrease in comparison with a NHMM biosensor. A low detection limit of 0.25 ng/mL (1.25 pM) is estimated when considering a noise level of 0.05 nm as the minimum detectable wavelength shift. The proposed method achieves high sensitivity and good reproducibility for CEA detection, which makes it a novel and viable approach for biomedical research and early clinical diagnostics.

Itaconic Acid Cross-Linked Biomolecule Immobilization Approach on Amine-Functionalized Silica Nanoparticles for Highly Sensitive Enzyme-Linked Immunosorbent Assay (ELISA)

Biomolecule immobilization on nanomaterials is attractive for biosensors since it enables the capture of a higher concentration of bioreceptor units while also serving as a transduction element. The technique could enhance the accuracy, specificity, and sensitivity of the analytical measurements of biomolecules. However, it was found that the limitation in chemically binding biomolecules on nanoparticle surfaces could only cross-link between the C-terminal and N-terminal. Here, we report the facile one-step synthesis of amine-functionalized silica nanoparticles (AFSNPs). (3-Aminopropyl)triethoxysilane was used as a precursor to modify the functional surface of nanoparticles via the Stöber process. The biomolecules were immobilized to the AFSNPs through itaconic acid, a novel cross-linker that binds between the N-terminal and N-terminal and potentially improves proteins and nucleic acid immobilization onto the nanoparticle surface. The newly developed immobilization approach on AFSNPs for biomolecular detection enhanced the efficiency of ELISA, resulting in increased sensitivity. It might also be easily used to identify different pathogens for clinical diagnostics.

Optical fiber surface plasmon resonance sensor using electroless-plated gold film for thrombin detection

This paper describes the simple and label-free detection of thrombin using optical fiber surface plasmon resonance (SPR) sensors based on gold films prepared by the cost-effective method of electroless plating. The plating conditions for simultaneously obtaining gold film on cylindrical core and end surfaces of an optical fiber suitable for measurement were optimized. The fabricated sensor exhibited a linear refractive index sensitivity of 2150 nm/RIU and 7.136 (a.u.)/RIU in the refractive index of 1.3329-1.3605 interrogated by resonance wavelength and amplitude methods respectively and a single wavelength monitoring method was proposed to investigate the sensing performance of this sensor. Polyadenine diblock and thiolated thrombin aptamers were immobilized on gold nanoparticles and gold films respectively to implement a sandwich optical fiber assay for thrombin. The developed optical fiber SPR sensors were successfully used in the determination of thrombin down to 0.56 nM over a wide range from 2 to 100 nM and showed good selectivity for thrombin, which indicated their potential clinical applications for biomedical samples.

A Novel Aptamer Biosensor Based on a Localized Surface Plasmon Resonance Sensing Chip for High-Sensitivity and Rapid Enrofloxacin Detection

Enrofloxacin, a fluoroquinolone widely used in animal husbandry, presents environmental and human health hazards due to its stability and incomplete hydrolysis leading to residue accumulation. To address this concern, a highly sensitive aptamer biosensor utilizing a localized surface plasmon resonance (LSPR) sensing chip and microfluidic technology was developed for rapid enrofloxacin residue detection. AuNPs were prepared by the seed method and the AuNPs-Apt complexes were immobilized on the chip by the sulfhydryl groups modified on the end of the aptamer. The properties and morphologies of the sensing chip and AuNPs-Apt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectrophotometer, and scanning electron microscope (SEM), respectively. The sensing chip was able to detect enrofloxacin in the range of 0.01-100 ng/mL with good linearity, and the relationship between the response of the sensing chip and the concentration was Δλ (nm) = 1.288log ConENR (ng/mL) + 5.245 (R2 = 0.99), with the limit of detection being 0.001 ng/mL. The anti-interference, repeatability, and selectivity of this sensing chip were studied in detail. Compared with other sensors, this novel aptamer biosensor based on AuNPs-Apt complexes is expected to achieve simple, stable, and economical application in the field of enrofloxacin detection.

Recent Progresses in Optical Biosensors for Interleukin 6 Detection

Interleukin 6 (IL-6) is pleiotropic cytokine with pathological pro-inflammatory effects in various acute, chronic and infectious diseases. It is involved in a variety of biological processes including immune regulation, hematopoiesis, tissue repair, inflammation, oncogenesis, metabolic control, and sleep. Due to its important role as a biomarker of many types of diseases, its detection in small amounts and with high selectivity is of particular importance in medical and biological fields. Laboratory methods including enzyme-linked immunoassays (ELISAs) and chemiluminescent immunoassays (CLIAs) are the most common conventional methods for IL-6 detection. However, these techniques suffer from the complexity of the method, the expensiveness, and the time-consuming process of obtaining the results. In recent years, too many attempts have been conducted to provide simple, rapid, economical, and user-friendly analytical approaches to monitor IL-6. In this regard, biosensors are considered desirable tools for IL-6 detection because of their special features such as high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current progresses in different types of optical biosensors as the most favorable types of biosensors for the detection of IL-6 are discussed, evaluated, and compared.

Sensitivity investigation of a biosensor with resonant coupling of propagating surface plasmons to localized surface plasmons in the near infrared region

Gold nanoparticles (AuNPs) can be used to improve the performance of propagating surface plasmon resonance (PSPR) refractive index sensors. The resonant coupling effect between PSPR and localized surface plasmon resonance (LSPR) supported by AuNPs on sensitivity remains to be elucidated in terms of evanescent field intensity and distribution. In this study, we directly compare the sensitivity of the PSPR sensor and the resonant coupling mode between the PSPR and LSPR sensors in the wavelength scanning mode. The sensitivity of PSPR can be significantly improved in the near-infrared region excitation wavelength. 1,6-Hexanedithiol was used to achieve a AuNP modified gold film (GF-AuNP). The PSPR excited by the prism coupling mechanism can effectively stimulate LSPR supported by AuNPs in the GF-AuNP, and then resonant coupling is generated. Compared with PSPR, the resonant coupling mode shows a decrease in penetration depth by 28 times and an increase in the surface electric field intensity by 4.6 times in the numerical simulations. The decrease in the penetration depth in the GF-AuNP is made at the expense of bulk sensitivity. The biosensing sensitivity of the GF-AuNP shows up to 7-fold improvement in the carcinoembryonic antigen immunoassay and the GF-AuNP is proven to be a better biosensor. The experimental measurements are in excellent agreement with the theoretical model. This study can be also considered as a guide for the design of plasmonic sensors for detecting multiple substances at different scales, such as cells and proteins.

Effect of Selenium Nanoparticle Size on IL-6 Detection Sensitivity in a Lateral Flow Device

Sepsis is the body's response to an infection. Existing diagnostic testing equipment is not available in primary care settings and requires long waiting times. Lateral flow devices (LFDs) could be employed in point-of-care (POC) settings for sepsis detection; however, they currently lack the required sensitivity. Herein, LFDs are constructed using 150-310 nm sized selenium nanoparticles (SeNPs) and are compared to commercial 40 nm gold nanoparticles (AuNPs) for the detection of the sepsis biomarker interleukin-6 (IL-6). Both 310 and 150 nm SeNPs reported a lower limit of detection (LOD) than 40 nm AuNPs (0.1 ng/mL compared to 1 ng/mL), although at the cost of test line visual intensity. This is to our knowledge the first use of larger SeNPs (>100 nm) in LFDs and the first comparison of the effect of the size of SeNPs on assay sensitivity in this context. The results herein demonstrate that large SeNPs are viable alternatives to existing commercial labels, with the potential for higher sensitivity than standard 40 nm AuNPs.

Single-Nanoparticle Differential Immunoassay for Multiplexed Gastric Cancer Biomarker Monitoring

Precision medicine demands the best application of multiple unambiguous biomarkers to bring uniform decisions in disease prognosis. The remarkable development of heterogeneous immunoassay greatly promotes precision medicine when combined with the biomarker combination strategy. Nevertheless, the cumbersome washing steps in heterogeneous immunoassay have inevitably compromised the accuracy because of the sample losses and nature change of the matrix, challenging the further exploration of a more facile and lower limit-of-detection analysis. The new methodologies with high throughputs and specificity are never out of date to provide simultaneous evaluations and uniform decisions on multiple analytes through a simple process. Herein, we propose a new wash-free immunoassay, named differential assay, for multiplexed biomarker monitoring. The method is based on counting the number difference of unbound nanoparticle tags before and after immunoreactions from a solid support (i.e., magnetic microsphere) by single-particle inductively coupled plasma mass spectrometry (sp-ICP-MS), discarding the tedious washing steps. We primarily explore the proof-of-concept proposal within two types (sandwich and competitive assay), demonstrating the good feasibility for further facile clinical practice. To provide efficient multiplexed evaluations, we synthesized PtNPs with four diameters and screened the most suitable size for efficient differential immunoassay. The wash-free strategy was successfully utilized in simultaneous serological biomarker (CA724, CA199, and CEA) evaluation, with results in good accordance with those measured by the clinical routine method. Potentially, the proposed differential bioassay can be regarded as a more facile and valuable tool in malignancy prognosis and cancer recurrence monitoring.

An immunogold single extracellular vesicular RNA and protein (Au SERP) biochip to predict responses to immunotherapy in non-small cell lung cancer patients

Conventional PD-L1 immunohistochemical tissue biopsies only predict 20%-40% of non-small cell lung cancer (NSCLC) patients that will respond positively to anti-PD-1/PD-L1 immunotherapy. Herein, we present an immunogold biochip to quantify single extracellular vesicular RNA and protein (Au SERP) as a non-invasive alternative. With only 20 μl of purified serum, PD-1/PD-L1 proteins on the surface of extracellular vesicles (EVs) and EV PD-1/PD-L1 messenger RNA (mRNA) cargo were detected at a single-vesicle resolution and exceeded the sensitivities of their bulk-analysis conventional counterparts, ELISA and qRT-PCR, by 1000 times. By testing a cohort of 27 non-responding and 27 responding NSCLC patients, Au SERP indicated that the single-EV mRNA biomarkers surpass the single-EV protein biomarkers in predicting patient responses to immunotherapy. Dual single-EV PD-1/PD-L1 mRNA detection differentiated responders from non-responders with an accuracy of 72.2% and achieved an NSCLC diagnosis accuracy of 93.2%, suggesting the potential for Au SERP to provide enhanced immunotherapy predictions and cancer diagnoses within the clinical setting.

Elucidating Sensitivity and Stability Relationship of Gold-Carbon Hybrid LSPR Sensors Using Principal Component Analysis

Sensitive localized surface plasmon resonance (LSPR) sensing is achieved using nanostructured geometries of noble metals which typically have dimensions less than 100 nm. Among the plethora of geometries and materials, the spherical geometries of gold (Au) are widely used to develop sensitive bio/chemical sensors due to ease of manufacturing and biofunctionlization. One major limitation of spherical-shaped geometries of Au, used for LSPR sensing, is their low refractive index (RI) sensitivity which is commonly addressed by adding another material to the Au nanostructures. However, the process of addition of new material on Au nanostructures, while retaining the LSPR of Au, often comes with a trade-off which is associated with the instability of the developed composite, especially in harsh chemical environments. Addressing this challenge, we develop a Au-graphene-layered hybrid (Au-G) with high stability (studied up to 2 weeks here) and enhanced RI sensitivity (a maximum of 180.1 nm/RIU) for generic LSPR sensing applications using spherical Au nanostructures in harsh chemical environments, involving organic solvents. Additionally, by virtue of principal component analysis, we correlate stability and sensitivity of the developed system. The relationship suggests that the shelf life of the material is proportional to its sensitivity, while the stability of the sensor during the measurement in liquid environment decreases when the sensitivity of the material is increased. Though we uncover this relationship for the LSPR sensor, it remains evasive to explore similar relationships within other optical and electrochemical transduction techniques. Therefore, our work serves as a benchmark report in understanding/establishing new correlations between sensing parameters.

Elongated nanoporous Au networks improve somatic cell direct conversion into induced dopaminergic neurons for Parkinson's disease therapy

The efficient production of dopaminergic neurons via the direct conversion of other cell types is of interest as a potential therapeutic approach for Parkinson's disease. This study aimed to investigate the use of elongated porous gold nanorods (AuNpRs) as an enhancer of cell fate conversion. We observed that AuNpRs promoted the direct conversion of fibroblasts into dopaminergic neurons in vivo and in vitro. The extent of conversion of fibroblasts into dopaminergic neurons depended on the porosity of AuNpRs, as determined by their aspect ratio. The mechanism underlying these results involves specific AuNpR-induced transcriptional changes that altered the expression of antioxidant-related molecules. The generation of dopaminergic neurons via the direct conversion method will open a new avenue for developing a therapeutic platform for Parkinson's disease treatment. STATEMENT OF SIGNIFICANCE: In this study, we applied modified gold nanoporous materials (AuNpRs) to the direct lineage reprogramming of dopaminergic neurons. The cell reprogramming process is energy-intensive, resulting in an excess of oxidative stress. AuNpRs facilitated the direct conversion of dopaminergic neurons by ameliorating oxidative stress during the reprogramming process. We have found this mechanistic clue from high throughput studies in this research work.

Selective Amplification of Plasmonic Sensor Signal for Cortisol Detection Using Gold Nanoparticles

Herein, gold nanoparticles (AuNP)-modified cortisol-imprinted (AuNP-MIP) plasmonic sensor was developed for signal amplification and real-time cortisol determination in both aqueous and complex solutions. Firstly, the sensor surfaces were modified with 3-(trimethoxylyl)propyl methacrylate and then pre-complex was prepared using the functional monomer N-methacryloyl-L-histidine methyl ester. The monomer solution was made ready for polymerization by adding 2-hydroxyethyl methacrylate to ethylene glycol dimethacrylate. In order to confirm the signal enhancing effect of AuNP, only cortisol-imprinted (MIP) plasmonic sensor was prepared without AuNP. To determine the selectivity efficiency of the imprinting process, the non-imprinted (AuNP-NIP) plasmonic sensor was also prepared without cortisol. The characterization studies of the sensors were performed with atomic force microscopy and contact angle measurements. The kinetic analysis of the AuNP-MIP plasmonic sensor exhibited a high correlation coefficient (R² = 0.97) for a wide range (0.01–100 ppb) with a low detection limit (0.0087 ppb) for cortisol detection. Moreover, the high imprinting efficiency (k′ = 9.67) of the AuNP-MIP plasmonic sensor was determined by comparison with the AuNP-NIP plasmonic sensor. All kinetic results were validated and confirmed by HPLC.

SPR-Based Sensor for the Early Detection or Monitoring of Kidney Problems

SPR-based technology has emerged as one of the most versatile optical tools for analyzing the binding mechanism of molecular interaction due to its inherent advantages in sensing applications, such as real-time, label-free, and high sensitivity characteristics. SPR is widely used in various fields, including healthcare, environmental management, and food-borne illness analysis. Meanwhile, kidney disease has grown to be one of the world's most serious public health problems in recent decades, resulting in physical degeneration and even death. As a result, several studies have published their findings regarding developing of reliable sensor technology based on the SPR phenomenon. However, an integrated and comprehensive discussion regarding the application of SPR-based sensors for detecting of kidney disease has not yet been found. Therefore, this review will discuss the recent advancements in the development of SPR-based sensors for monitoring kidney-related diseases. Numerous SPR configurations will be discussed, including Kretschmann, Otto, optical fiber-based SPR, and LSPR, which are all used to detect analytes associated with kidney disease, including urea, creatinine, glucose, uric acid, and dopamine. This review aims to show the broad application of SPR sensors which encouraged the development of SPR sensors for kidney problems monitoring.

Two Biosensors for the Determination of Interleukin-6 in Blood Plasma by Array SPRi

Interleukin-6 (IL-6) is a biomarker of inflammation, the advanced stage of COVID-19, and several cancers, including ovarian cancer. Two biosensors for the determination of IL-6 in blood plasma by array SPRi have been developed. One of these biosensors consists of the mouse monoclonal anti-IL-6 antibody as the receptor immobilized via the cysteamine linker. The second contains galiellalactone as the receptor, being an inhibitor specific for IL-6, immobilized via octadecanethiol (ODM) as the linker. Both biosensors are specific for IL-6. The biosensor with the antibody as the receptor gives a linear analytical response between 3 (LOQ) and 20 pg mL⁻¹ and has a precision between 8% and 9.8% and recovery between 97% and 107%, depending on the IL-6 concentration. The biosensor with galiellalactone as the receptor gives a linear analytical response between 1.1 (LOQ) and 20 pg mL⁻¹, and has a precision between 3.5% and 9.3% and recovery between 101% and 105%, depending on IL-6 concentration. Both biosensors were validated. Changes in IL-6 concentration in blood plasma before and after resection of ovarian tumor and endometrial cyst, as determined by the two developed biosensors, are given as an example of a real clinical application.

Standard-free single magnetic bead evaluation: a stable nanoplatform for prostate disease differentiation

Explicit interpretation of heterogeneity between prostate-specific antigen (PSA) subtypes is essential for prostate cancer differentiation during different disease courses, whereas a universal protocol with uniform criteria is still lacking across the globe. In this work, a standard-free single magnetic bead (SMB) nanoplatform utilizing metal nanoparticles with optimal diameters was proposed for prostate disease differentiation in a 134-donor model. The inaccuracy of detection in absolute quantification was diminished via evaluations of metal intensities on the single magnetic bead. The intrinsic proportion of fPSA in tPSA was successfully evaluated by direct use of the Pt to Au intensity ratio (Pt/Au ratio), exhibiting better differentiation between healthy and unhealthy, benign prostatic hyperplasia (BPH) and cancer individuals compared with solo fPSA or tPSA. We generated thresholds respectively for prostate disease differentiation, envisioning that this standard-free SMB nanoplatform would establish a standardized methodology with uniform criteria worldwide in cancer diagnosis, staging, and postoperative assessments.

Nano-engineered materials for sensing food pollutants: Technological advancements and safety issues

Food spoilage and safety are key concerns of the modern food sector. Among them, several types of polluting agents are the prime grounds of food deterioration. In this context, nanotechnology-based measures are setting new frontiers to strengthen food applications. Herein, we summarize the nanotechnological dimension of the food industry for both processing and packaging applications. Active bioseparation, smart delivery, nanoencapsulation, nutraceuticals, and nanosensors for biological detection are a few emerging topics of nanobiotechnology in the food sector. The development of functional foods is another milestone set by food nanotechnology by building the link between humans and diet. However, the establishment of optimal intake, product formulations, and delivery matrices, the discovery of beneficial compounds are a few of the key challenges that need to be addressed. Nanotechnology provides effective solutions for the aforementioned problem giving various novel nanomaterials and methodologies. Various nanodelivery systems have been designed, e.g., cochleate, liposomes, multiple emulsions, and polysaccharide-protein coacervates. However, their real applications in food sciences are very limited. This review also provides the status and outlook of nanotechnological systems for future food applications.

Polarization-controlled single-particle scattering imaging spectroscopy using waveguide excitation

An imaging spectroscopic system that enables spatially-resolved detection of single-particle scattering with polarization-controlled waveguide excitation scheme is presented. The detected microscopic images of inhomogeneous nanostructures are recorded in a time sequence into a data cube based on a Michelson interferometer. The interferograms on selected pixels are Fourier-transformed into multiple spectra. The waveguide excitation scheme is presented for both transmission and reflection measurements while the dark-field excitation scheme is presented in transmission measurements for comparison. Gold nanoparticles, nanorods, and particles on film are utilized in the detection of polarization-dependent spectra. Measurement results are verified with the finite-difference time-domain (FDTD) simulations. The polarization-controlled coupling conditions in nanorods and particle-on-film systems are discussed with simulated field distributions around the nanostructures.

Preparation of a disposable electrochemiluminescence sensor chip based on an MXene-loaded ruthenium luminescent agent and its application in the detection of carcinoembryonic antigens

We developed a novel type of disposable ECL sensor chip for CEA detection in serum samples of healthy humans and cancer patients. The disposable ECL sensor chip has many advantages including convenience, rapid detection, low cost, and easy mass production.

Detecting attomolar concentrations of microRNA related to myelodysplastic syndromes in blood plasma using a novel sandwich assay with nanoparticle release

Microribonucleic acids (miRNAs) are short noncoding ribonucleic acids that have been linked with a multitude of human diseases including lung, breast, and hematological cancers. In this work, we present a novel, extremely sensitive assay for the label-free optical biosensor-based detection of miRNAs, which is based on the oligonucleotide-triggered release of nanoparticles from a sensor surface. We combine this assay (herein referred to as the nanoparticle-release (NPR) assay) with a surface plasmon resonance biosensor and show that the assay is able to enhance the specific sensor response associated with the binding of target miRNA while suppressing the interfering effects caused by the non-specific binding. We apply the assay to the detection of miRNAs related to myelodysplastic syndromes (miR-125b, miR-16) in blood plasma and demonstrate that the assay enables detection of miR-125b with a limit of detection (LOD) of 349 aM (corresponding to the lowest detectable amounts of 419 zmol). The achieved LOD is better by a factor of ∼100 when compared to the conventional nanoparticle-enhanced sandwich assay. Moreover, we demonstrate that the NPR assay may be combined with time-division multiplexing for the multiplexed miRNA detection.

Gold Nanoparticles: Biosynthesis and Potential of Biomedical Application

Gold nanoparticles (AuNPs) are extremely promising objects for solving a wide range of biomedical problems. The gold nanoparticles production by biological method ("green synthesis") is eco-friendly and allows minimization of the amount of harmful chemical and toxic byproducts. This review is devoted to the AuNPs biosynthesis peculiarities using various living organisms (bacteria, fungi, algae, and plants). The participation of various biomolecules in the AuNPs synthesis and the influence of size, shapes, and capping agents on the functionalities are described. The proposed action mechanisms on target cells are highlighted. The biological activities of "green" AuNPs (antimicrobial, anticancer, antiviral, etc.) and the possibilities of their further biomedical application are also discussed.

CRISPR/Cas-powered nanobiosensors for diagnostics

CRISPR diagnostics (CRISPR-Dx) offer a wide range of enhancements compared to traditional nanobiosensors by taking advantage of the excellent trans-cleavage activity of the CRISPR/Cas systems. However, the single-stranded DNA/RNA reporters of the current CRISPR-Dx suffer from poor stability and limited sensitivity, which make their application in complex biological environments difficult. In comparison, nanomaterials, especially metal nanoparticles, exhibits robust stability and desirable optical and electrocatalytical properties, which make them ideal as reporter molecules. Therefore, biosensing research is moving towards the use of the trans-cleavage activity of CRISPR/Cas effectors on metal nanoparticles and apply the new phenomenon to develop novel nanobiosensors to target various targets such as viral infections, genetic mutations and tumor biomarkers, by using different sensing methods, including, but not limited to fluorescence, luminescence resonance, colorimetric and electrochemical signal readout. In this review, we explore some of the most recent advances in the field of CRISPR-powered nanotechnological biosensors. Demonstrating high accuracy, sensitivity, selectivity and versatility, nanobiosensors along with CRISPR/Cas technology offer tremendous potential for next-generation diagnostics of multiple targets, especially at the point of care and without any target amplification.

Biosensor Based Immunoassay: A New Approach for Serotyping of Toxoplasma gondii

Toxoplasmosis is the most reported parasitic zoonosis in Europe, with implications in human health and in the veterinary field. There is an increasing need to develop serotyping of Toxoplasma gondii (T. gondii) in view of greater sensitivity and efficiency, through the definition of new targets and new methodologies. Nanotechnology is a promising approach, with impact in the development of point-of-care devices. The aim of this work was to develop a simple but highly efficient method for Toxoplasma gondii serotyping based on gold nanoparticles. A simple colorimetric method was developed using gold nanoparticles modified with the synthetic polymorphic peptide derived from GRA6 antigen specific for type II T. gondii. The method of preparation of the gold nanoprobes and the experimental conditions for the detection were found to be critical for a sensitive discrimination between positive and negative sera. The optimized method was used to detect antibodies anti-GRA6II both in mice and human serum samples. These results clearly demonstrate that a biosensor-based immunoassay using AuNPs conjugated with polymorphic synthetic peptides can be developed and used as a serotyping device

Amplification-free Detection of Cytomegalovirus miRNA Using a Modification-free Surface Plasmon Resonance Biosensor

Cytomegalovirus (CMV) is the most frequent cause of congenital infection worldwide; congenital CMV may lead to significant mortality, morbidity, or long-term sequelae, such as sensorineural hearing loss. The current study presents a newly designed surface plasmon resonance (SPR) biosensor for CMV-specific microRNAs that does not involve extra care for receptor immobilization or treatment to prevent fouling on bare gold surfaces. The modification-free approach, which utilizes a poly-adenine [poly(A)]-Au interaction, exhibited a high affinity that was comparable to that of the gold-sulfur (Au-S) interaction. In addition, magnetic nanoparticles (MNPs) were used to separate the analyte from complex sample matrixes that significantly reduced nonspecific adsorption. Moreover, the MNPs also played an important role in SPR signal amplification due to the binding-induced change in the refractive index. Our SPR biosensing platform was used successfully for the multi-detection of the microRNAs, UL22A-5p, and UL112-3p, which were associated with CMV. Our SPR biosensor offered the detection limits of 108 fM and 24 fM for UL22A-5p and UL112-3p, respectively, with an R² of 0.9661 and 0.9985, respectively. The precision of this biosensor has an acceptable CV (coefficient of variation) value of <10%. In addition, our sensor is capable of discriminating between serum samples collected from healthy and CMV-infected newborns. Taken together, we believe that our newly developed SPR biosensing platform is a promising alternative for the diagnosis of CMV-specific microRNA in clinical settings, and its application for the detection of other miRNAs may be extended further.

Potential of surface plasmon resonance biosensors in cancer detection

A review is made of 71 papers on surface plasmon resonance biosensors, published between 2005 and 2020, mostly in the last decade. The reviewed papers are divided into two groups, depending on the validation of the developed biosensor. Validated biosensors are briefly characterized, while those that are not validated are listed in a table. Focus is placed on applications of SPR biosensors in testing the effectiveness of cancer markers and in the discovery of new cancer markers. Seven new markers are proposed, two of them having high sensitivity and diagnostic selectivity as determined by ROC curves. Papers concerning the determination of micro RNA and large particles such as vesicles, exosomes and cancer cells are also reviewed.

Drug-Based Gold Nanoparticles Overgrowth for Enhanced SPR Biosensing of Doxycycline

In clinical chemistry, frequent monitoring of drug levels in patients has gained considerable importance because of the benefits of drug monitoring on human health, such as the avoidance of high risk of over dosage or increased therapeutic efficacy. In this work, we demonstrate that the drug doxycycline can act as an Au nanoparticle (doxy-AuNP) growth and capping agent to enhance the response of a surface plasmon resonance (SPR) biosensor for this drug. SPR analysis revealed the high sensitivity of doxy-AuNPs towards the detection of free doxycycline. More specifically, doxy-AuNPs bound with protease-activated receptor-1 (PAR-1) immobilized on the SPR sensing surface yield the response in SPR, which was enhanced following the addition of free doxy (analyte) to the solution of doxy-AuNPs. This biosensor allowed for doxycycline detection at concentrations as low as 7 pM. The study also examined the role of colloidal stability and growth of doxy-AuNPs in relation to the response-enhancement strategy based on doxy-AuNPs. Thus, the doxy-AuNPs-based SPR biosensor is an excellent platform for the detection of doxycycline and demonstrates a new biosensing scheme where the analyte can provide enhancement.

An immunosensor for the determination of carcinoembryonic antigen by Surface Plasmon Resonance imaging

Carcinoembryonic antigen (CEA) is one of the biomarkers most commonly used to determine tumor activity. In this work, a Surface Plasmon Resonance imaging (SPRi) immunosensor was developed. The immunosensor consists of a cysteamine linker attached to a gold chip and mouse monoclonal anti-CEA antibody bonded by the "EDC/NHS protocol". The formation of successive immunosensor layers was confirmed by AFM measurements. The concentration of the antibody was optimized. The linear response range of the developed immunosensor is between 0.40 and 20 ng mL^-1, and it is suitable for CEA measurement in both blood cancer patients and healthy individuals. Only 3 μL of serum or plasma sample is required, and no preconcentration is used. The method has a precision of 2-16%, a recovery of 101-104% depending on CEA concentration, a detection limit of 0.12 ng mL^-1 and a quantification limit of 0.40 ng mL^-1. The method is selective (with respect to albumin, leptin, interleukin 6, metalloproteinase-1, metallopeptidase inhibitor 1 and CA 125/MUC16) and it was validated by comparison with the standard electrochemiluminescence method on a series of colorectal cancer blood samples.

A plasmonic fiberoptic absorbance biosensor for mannose-capped lipoarabinomannan based tuberculosis diagnosis

Tuberculosis (TB) is a resurgent infectious disease affecting a large number of people in the developing countries. An on-site, affordable diagnostic screening at an early-stage for an immediate anti-TB treatment is known to tremendously minimize the high mortality rates. Lipoarabinomannan (LAM), a surface glycolipid, has been identified as a potential TB biomarker present in urine at ultra-low concentrations of a few fg/mL. Here, we report a plasmonic fiber optic absorbance biosensor (P-FAB) strategy for mannosylated LAM (Man-LAM or Mtb LAM) detection down to attomolar concentrations. It involves a plasmonic sandwich immunoassay on a U-bent fiber optic probe with gold plasmonic (AuNP) labels functionalized with anti-Mtb LAM immunoglobulin M (IgM) and anti-Mtb LAM IgG respectively. The Mtb LAM is quantified in terms of absorption of light passing through the fiber probe using a green LED and a photodetector. The choice of fiber optic probes (fused silica versus polymer), the optimum size (20, 40, 60 and 80 nm) and concentration (2 × , 10 × , and 20 × ) of AuNP labels were investigated to obtain high sensitivity and lower limits of analyte detection (LoD). P-FAB with a simple LED-photodetector pair, 200 μm fused silica U-bent fiber probe and 60 nm (20 × ) AuNP labels gave LoDs down to 1 fg/mL and 10 fg/mL in the buffer and synthetic urine respectively. Moreover, the anti-Mtb LAM IgM bound sensor probes and the AuNP reagent stored at 4 °C were stable up to 45 days. P-FAB based Mtb LAM sensor demonstrates its potential for an on-site TB diagnosis.

Advantages of Highly Spherical Gold Nanoparticles as Labels for Lateral Flow Immunoassay

The use of lateral flow immunoassays (LFIAs) for rapid on-site testing is restricted by their relatively high limit of detection (LoD). One possible way to decrease the LoD is to optimize nanoparticle properties that are used as labels. We compare two types of Au nanoparticles: usual quasispherical gold nanoparticles (C-GNPs), obtained by the Turkevich–Frens method, and superspherical gold nanoparticles (S-GNPs), obtained by a progressive overgrowth technique. Average diameters were 18.6–47.5 nm for C-GNPs and 20.2–90.4 nm for S-GNPs. Cardiomarker troponin I was considered as the target analyte. Adsorption and covalent conjugation with antibodies were tested for both GNP types. For C-GNPs, the minimal LoD was obtained with 33.7 nm nanoparticles, reaching 12.7 ng/mL for covalent immobilization and 9.9 ng/mL for adsorption. The average diameter of S-GNPs varied from 20.2 to 64.5 nm, which resulted in a decrease in LoD for an LFIA of troponin I from 3.4 to 1.2 ng/mL for covalent immobilization and from 2.9 to 2.0 ng/mL for adsorption. Thus, we obtained an 8-fold decrease in LoD (9.9 to 1.2 ng/mL) by using S-GNPs. This effect can be related to more effective antibody immobilization and improved S-GNP optical properties. The obtained results can improve LFIAs for various practically significant analytes.

Microbe-Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

Microbe-mediated mineralization is ubiquitous in nature, involving bacteria, fungi, viruses, and algae. These mineralization processes comprise calcification, silicification, and iron mineralization. The mechanisms for mineral formation include extracellular and intracellular biomineralization. The mineral precipitating capability of microbes is often harnessed for green synthesis of metal nanoparticles, which are relatively less toxic compared with those synthesized through physical or chemical methods. Microbe-mediated mineralization has important applications ranging from pollutant removal and nonreactive carriers, to other industrial and biomedical applications. Herein, the different types of microbe-mediated biomineralization that occur in nature, their mechanisms, as well as their applications are elucidated to create a backdrop for future research.

Numerical evaluation of polyethylene glycol ligand conjugation to gold nanoparticle surface using ToF-SIMS and statistical analysis

Nanoparticles (NPs) are substances between 1 and 100 nm in size. They have been the subject of numerous studies because of their potential applications in a wide range of fields such as cosmetics, electronics, medicine, and food. For biological applications of nanoparticles, they are usually coated with a substance capable of preventing agglomeration of the nanoparticles and nonspecific binding and exhibiting water-solubility characteristics with specific immobilized (bio)molecules. In order to evaluate the chemical properties of the surface-modified nanoparticles for bioapplications, including drug delivery, a simple and reliable method for the analysis of the presence of the surface chemicals and the ligand states of the nanoparticles is necessary. In this study, the authors numerically evaluated the extent of polyethylene glycol (PEG) ligand conjugation on AuNPs by concurrently adopting a microliquid inkjet printing system for sampling of the PEGylated AuNPs solution and ToF-SIMS imaging together with statistical analysis. The statistical correlation values calculated from the signals of PEG and Au measured by ToF-SIMS imaging on the sample spots made by a microliquid inkjet printing system showed better reproducibility and improved correlation values compared to the pipet spotting. Their improved method will be useful to evaluate ligand-conjugated nanoparticles for quality control of each conjugation process.

Enhanced sensitivity in graphene-based SPR biosensors using electrical bias

A theoretical framework to increase the sensitivity of graphene-based surface plasmon resonance (SPR) biosensors by the application of electrical bias voltage across the sensor surface is presented. Graphene layers deposited on thin gold film (50 nm) form the sensor surface system where the surface plasmon is excited. The real and imaginary parts of the refractive index of this gold-graphene system can be controlled by tuning its chemical potential using electrical modulation. Numerical calculations show a promising method to enhance the sensitivity of graphene-based SPR biosensors.

High-performance plasmonic refractive index sensors via synergy between annealed nanoparticles and thin films

Plasmonic nanostructure-based refractive index (RI) sensors are the core component of biosensor systems and play an increasingly important role in the diagnosis of human disease. However, the costs of traditional plasmonic RI sensors are not acceptable to everyone due to their expensive fabrication process. Here, a novel low-cost and high-performance visible-light RI sensor with a particle-on-film configuration was experimentally demonstrated. The sensor was fabricated by transferring annealed Au nanoparticles (NPs) onto a thin gold film with polymethyl methacrylate (PMMA) as a support. RI sensitivities of approximately 209 nm/RIU and 369 nm/RIU were achieved by reflection and transmission spectrum measurements, respectively. The high sensitivity is due to the strong plasmon-mediated energy confinement within the interface between the particles and the film. The possibility of wafer-scale production and high working stability achieved by the transfer process, together with the high sensitivity to the environmental RI, provides an extensive impact on the realization of universal biosensors for biological applications.

Plasmonic nucleotide hybridization chip for attomolar detection: localized gold and tagged core/shell nanomaterials

We report a large amplification of surface plasmon signals for a double hybridization microarray chip assembly that bridges localized gold and detection probe-carrying-core/shell Fe₃O₄@Au nanoparticles for detection of as low as 80 aM miRNA-155 marker in solution. The plasmonic wavelength match of the gold shell with surface localized gold nanoparticles and the additional scattering band of the core/shell material in resonance with the incident 800 nm light source are the underlying factors for the observed remarkable analyte signal at ultra-low (10^-18 order) concentrations.

Nanoplasmonic Approaches for Sensitive Detection and Molecular Characterization of Extracellular Vesicles

All cells release a multitude of nanoscale extracellular vesicles (nEVs) into circulation, offering immense potential for new diagnostic strategies. Yet, clinical translation for nEVs remains a challenge due to their vast heterogeneity, our insufficient ability to isolate subpopulations, and the low frequency of disease-associated nEVs in biofluids. The growing field of nanoplasmonics is poised to address many of these challenges. Innovative materials engineering approaches based on exploiting nanoplasmonic phenomena, i.e., the unique interaction of light with nanoscale metallic materials, can achieve unrivaled sensitivity, offering real-time analysis and new modes of medical and biological imaging. We begin with an introduction into the basic structure and function of nEVs before critically reviewing recent studies utilizing nanoplasmonic platforms to detect and characterize nEVs. For the major techniques considered, surface plasmon resonance (SPR), localized SPR, and surface enhanced Raman spectroscopy (SERS), we introduce and summarize the background theory before reviewing the studies applied to nEVs. Along the way, we consider notable aspects, limitations, and considerations needed to apply plasmonic technologies to nEV detection and analysis.

Two-color surface plasmon resonance nanosizer for gold nanoparticles

We study the potentialities of a two-color Surface Plasmon Resonance (SPR) spectroscopy nanosizer by monitoring the assembling of a colloidal dispersion of citrate stabilized gold nanoparticles (AuNPs) on SiO₂ surface. When the AuNPs/water composite's optical density layer is negligible and the electron mean-free path limitation is taken into account in the AuNPs' dielectric constant;s formulation, the surface density σ of the nanoparticle array and the statistical mean size <r> of the nanoparticles can be straightly determined by using two-color SPR spectroscopy in the context of Maxwell's Garnett theory. The optical method, demonstrated experimentally for AuNPs with a nominal mean diameter of 15 nm, can, theoretically, be extended to bigger nanoparticles, based on a simple scaling relation between the extinction cross section of the single nanoparticle σ_ext and the surface density σ. The experimental results, comparable to those obtained by AFM, transmission electron microscopy and dynamic light scattering technique, establish a novel insight on the SPR spectroscopy's potential to accurately characterize nanomaterials.

Peptide Functionalization of Gold Nanoparticles for the Detection of Carcinoembryonic Antigen in Blood Plasma via SPR-Based Biosensor

Nanoparticles functionalized with specific biological recognition molecules play a major role for sensor response enhancement in surface plasmon resonance (SPR) based biosensors. The functionalization procedure of such nanoparticles is crucial, since it influences their interactions with the environment and determines their applicability to biomolecular detection in complex matrices. In this work we show how the ζ-potential (Zpot) of bio-functionalized gold spherical NPs (Bio-NPs) is related to the SPR sensor response enhancement of an immune-sandwich-assay for the detection of the carcinoembryonic antigen (CEA), a cancer marker for colorectal carcinomas. In particular, we prepare bio-functional nanoparticles by varying the amount of peptide (either streptavidin or antibody against CEA) bound on their surface. Specific and non-specific sensor responses, reproducibility, and colloidal stability of those bio-functional nanoparticles are measured via SPR and compared to ζ-potential values. Those parameters are first measured in buffer solution, then measured again when the surface of the biosensor is exposed to blood plasma, and finally when the nanoparticles are immersed in blood plasma and flowed overnight on the biosensor. We found that ζ-potential values can guide the design of bio-functional NPs with improved binding efficiency and reduced non-specific sensor response, suitable reproducibility and colloidal stability, even in complex matrixes like blood plasma.

Limits of the Effective Medium Theory in Particle Amplified Surface Plasmon Resonance Spectroscopy Biosensors

The resonant wave modes in monomodal and multimodal planar Surface Plasmon Resonance (SPR) sensors and their response to a bidimensional array of gold nanoparticles (AuNPs) are analyzed both theoretically and experimentally, to investigate the parameters that rule the correct nanoparticle counting in the emerging metal nanoparticle-amplified surface plasmon resonance (PA-SPR) spectroscopy. With numerical simulations based on the Finite Element Method (FEM), we evaluate the error performed in the determination of the surface density of nanoparticles σ when the Maxwell-Garnett effective medium theory is used for fast data processing of the SPR reflectivity curves upon nanoparticle detection. The deviation increases directly with the manifestations of non-negligible scattering cross-section of the single nanoparticle, dipole-dipole interactions between adjacent AuNPs and dipolar interactions with the metal substrate. Near field simulations show clearly the set-up of dipolar interactions when the dielectric thickness is smaller than 10 nm and confirm that the anomalous dispersion usually observed experimentally is due to the failure of the effective medium theories. Using citrate stabilized AuNPs with a nominal diameter of about 15 nm, we demonstrate experimentally that Dielectric Loaded Waveguides (DLWGs) can be used as accurate nanocounters in the range of surface density between 20 and 200 NP/µm², opening the way to the use of PA-SPR spectroscopy on systems mimicking the physiological cell membranes on SiO₂ supports.

Surface Plasmon Enhanced Light Scattering Biosensing: Size Dependence on the Gold Nanoparticle Tag

Surface plasmon enhanced light scattering (SP-LS) is a powerful new sensing SPR modality that yields excellent sensitivity in sandwich immunoassay using spherical gold nanoparticle (AuNP) tags. Towards further improving the performance of SP-LS, we systematically investigated the AuNP size effect. Simulation results indicated an AuNP size-dependent scattered power, and predicted the optimized AuNPs sizes (i.e., 100 and 130 nm) that afford extremely high signal enhancement in SP-LS. The maximum scattered power from a 130 nm AuNP is about 1700-fold higher than that obtained from a 17 nm AuNP. Experimentally, a bio-conjugation protocol was developed by coating the AuNPs with mixture of low and high molecular weight PEG molecules. Optimal IgG antibody bioconjugation conditions were identified using physicochemical characterization and a model dot-blot assay. Aggregation prevented the use of the larger AuNPs in SP-LS experiments. As predicted by simulation, AuNPs with diameters of 50 and 64 nm yielded significantly higher SP-LS signal enhancement in comparison to the smaller particles. Finally, we demonstrated the feasibility of a two-step SP-LS protocol based on a gold enhancement step, aimed at enlarging 36 nm AuNPs tags. This study provides a blue-print for the further development of SP-LS biosensing and its translation in the bioanalytical field.

Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/Pc Configuration and Sensitivity

Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface, because of the difficulty of removing adsorbed materials, and degradation of the sensor surface during surface cleaning and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of my approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and layered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct face-centered-cubic (fcc)-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of <100 Oersted (Oe). The sensor showed a maximum sensitivity of 5.5 × 104%/RIU (refractive index unit) for water–ethanol media and the highest detection level of 2.5 × 10−6 for water-pentanol media as the protective layer is increased from 0 to 15 nm.

Cytokeratins Biosensing Using Tilted Fiber Gratings

Optical fiber gratings have widely proven their applicability in biosensing, especially when they are coupled with antibodies for specific antigen recognition. While this is customarily done with fibers coated by a thin metal film to benefit from plasmonic enhancement, in this paper, we propose to study their intrinsic properties, developing a label-free sensor for the detection of biomarkers in real-time without metal coatings for surface plasmon resonances. We focus on the inner properties of our modal sensor by immobilizing receptors directly on the silica surface, and reporting the sensitivity of bare tilted fiber Bragg gratings (TFBGs) used at near infrared wavelengths. We test different strategies to build our sensing surface against cytokeratins and show that the most reliable functionalization method is the electrostatic adsorption of antibodies on the fiber, allowing a limit of detection reaching 14 pM by following the guided cladding modes near the cut-off area. These results present the biodetection performance that TFBGs bring through their modal properties for different functionalizations and data processing strategies.

Nanomaterials and phase sensitive based signal enhancment in surface plasmon resonance

Measurement of small molecules in extremely dilute concentrations of analyte play an important role in different issues ranging from food industry to biological, pharmaceutical and therapeutical applications. Surface plasmon resonance (SPR) sensors can be a suitable choice for detection of small molecules based on interactions with biomolecules. However, sensitivity of the system for detection of these molecules is very low. Improving sensitivity has been a challenge for years. Therefore, different methods have been used to enhance SPR signals. The SPR signal enhancement using numerous nanomaterials has provided exciting results. Among various nanomaterials, metal nanoparticles (for instance gold, silver and magnetic nanoparticles), quantum dots, nanorads, and carbon-based nanostructures have got much attention due to ease in fabrication, appropriate size and shape. In addition to the advantages provided by using nanomaterials, signal enhancement provided by the appropriate use of phase information of the reflected light could be also important to improve SPR sensitivity. Phase-sensitive SPR sensors are able to detect infinitesimal changes in external properties of target while traditional type of SPR cannot demonstrate these changes. This article provides an overview on signal enhancment in SPR using nanomaterials and properties of light. We also discuss on recent progresses of the field, describing basic concepts concerning nanostructures as well as phase-sensitive sensors as platform for enhancement of signal in SPR.

Mining the Potential of Label-Free Biosensors for In Vitro Antipsychotic Drug Screening

The pharmaceutical industry is facing enormous challenges due to high drug attribution rates. For the past decades, novel methods have been developed for safety and efficacy testing, as well as for improving early development stages. In vitro screening methods for drug-receptor binding are considered to be good alternatives for decreasing costs in the identification of drug candidates. However, these methods require lengthy and troublesome labeling steps. Biosensors hold great promise due to the fact that label-free detection schemes can be designed in an easy and low-cost manner. In this paper, for the first time in the literature, we aimed to compare the potential of label-free optical and impedimetric electrochemical biosensors for the screening of antipsychotic drugs (APDs) based on their binding properties to dopamine receptors. Particularly, we have chosen a currently-used atypical antipsychotic drug (Buspirone) for investigating its dopamine D3 receptor (D3R) binding properties using an impedimetric biosensor and a nanoplasmonic biosensor. Both biosensors have been specifically functionalized and characterized for achieving a highly-sensitive and reliable analysis of drug-D3R binding. Our biosensor strategies allow for comparing different affinities against the D3R, which facilitates the identification of strong or weak dopamine antagonists via in vitro assays. This work demonstrates the unique potential of label-free biosensors for the implementation of cost-efficient and simpler analytical tools for the screening of antipsychotic drugs.

A Localized Surface Plasmon Resonance Sensor Using Double-Metal-Complex Nanostructures and a Review of Recent Approaches

From active developments and applications of various devices to acquire outside and inside information and to operate based on feedback from that information, the sensor market is growing rapidly. In accordance to this trend, the surface plasmon resonance (SPR) sensor, an optical sensor, has been actively developed for high-sensitivity real-time detection. In this study, the fundamentals of SPR sensors and recent approaches for enhancing sensing performance are reported. In the section on the fundamentals of SPR sensors, a brief description of surface plasmon phenomena, SPR, SPR-based sensing applications, and several configuration types of SPR sensors are introduced. In addition, advanced nanotechnology- and nanofabrication-based techniques for improving the sensing performance of SPR sensors are proposed: (1) localized SPR (LSPR) using nanostructures or nanoparticles; (2) long-range SPR (LRSPR); and (3) double-metal-layer SPR sensors for additional performance improvements. Consequently, a high-sensitivity, high-biocompatibility SPR sensor method is suggested. Moreover, we briefly describe issues (miniaturization and communication technology integration) for future SPR sensors.