Myoglobin immunoassay based on metal particle-enhanced fluorescence

Integrative plasmonics: optical multi-effects and acousto-electric-thermal fusion for biosensing, energy conversion, and photonic circuits

Surface plasmons, a unique optical phenomenon arising at the interface between metals and dielectrics, have garnered significant interest across fields such as biochemistry, materials science, energy, optics, and nanotechnology. Recently, plasmonics is evolving from a focus on "classical plasmonics," which emphasizes fundamental effects and applications, to "integrative plasmonics," which explores the integration of plasmonics with multidisciplinary technologies. This review explores this evolution, summarizing key developments in this technological shift and offering a timely discussion on the fusion mechanisms, strategies, and applications. First, we examine the integration mechanisms of plasmons within the realm of optics, detailing how fundamental plasmonic effects give rise to optical multi-effects, such as plasmon-phonon coupling, nonlinear optical effects, electromagnetically induced transparency, chirality, nanocavity resonance, and waveguides. Next, we highlight strategies for integrating plasmons with technologies beyond optics, analyzing the processes and benefits of combining plasmonics with acoustics, electronics, and thermonics, including comprehensive plasmonic-electric-acousto-thermal integration. We then review cutting-edge applications in biochemistry (molecular diagnostics), energy (harvesting and catalysis), and informatics (photonic integrated circuits). These applications involve surface-enhanced Raman scattering (SERS), surface-enhanced infrared absorption (SEIRA), surface-enhanced fluorescence (SEF), chirality, nanotweezers, photoacoustic imaging, perovskite solar cells, photocatalysis, photothermal therapy, and triboelectric nanogenerators (TENGs). Finally, we conclude with a forward-looking perspective on the challenges and future of integrative plasmonics, considering advances in mechanisms (quantum effects, spintronics, and topology), materials (Dirac semimetals and hydrogels), technologies (machine learning, edge computing, in-sensor computing, and neuroengineering), and emerging applications (5G, 6G, virtual reality, and point-of-care testing).

Biomimetic Prussian Blue Sensor for Ultrasensitive Direct Detection of Myoglobin

This research presents a novel, cost-effective, and scalable approach for the direct detection of myoglobin (Myo) in point-of-care (PoC) applications. In this strategy, redox-active Prussian Blue nanocubes (PBNCs) are applied to a disposable platinum screen-printed electrode (Pt-SPE). Subsequently, a biomimetic sensing layer is generated by electropolymerization of ortho-phenylenediamine (o-PD) in the presence of Myo, which forms molecularly imprinted polymer (MIP) sites by cyclic voltammetry (CV). The electropolymerization process takes place in a potential range of -0.2 V to +0.8 V, for five cycles at a scan rate of 50 mV/s, in a 10 mmol/L o-PD solution. After polymerization, the electrode is incubated in trypsin for 2 h to create Myo-specifically imprinted cavities. The structural and morphological properties of the biomimetic layer were analyzed by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The direct detection of Myo was analyzed by differential pulse voltammetry (DPV). The results showed a linear response to Myo concentrations ranging from 1.0 ag/mL to 10 ng/mL, a limit of detection (LOD) of 0.76 ag/mL, and a R2 value of 0.9775. The absence of an external liquid redox probe simplifies the sensor design, improves portability, and reduces the complexity of the assay, making it more suitable for PoC.

Silver Nanoparticles Improve Fluorophore Photostability: Application to a Hypericin Study

Protection against the negative effects of solar radiation involves using cosmetics with a UV filter, but visible radiation can also have negative effects. We use dietary supplements and take medications; unfortunately, many of them contain substances that degrade under the influence of visible light, which transform into chemical compounds harmful to health. Manufacturers often include information on the prohibition of exposure to sunlight on the packaging, but consumers often do not read the product leaflet. The solution to this problem may be the addition of silver particles to preparations. In the presented article, we proposed the use of silver nanoparticles to reduce the photobleaching and photoreaction of fluorophore, while increasing the fluorescence intensity. For our research, we used a compound that is particularly sensitive to radiation: hypericin.

Biosensing Platforms for Cardiac Biomarker Detection

Myocardial infarction (MI) is a cardiovascular disease that occurs when there is an elevated demand for myocardial oxygen as a result of the rupture or erosion of atherosclerotic plaques. Globally, the mortality rates associated with MI are steadily on the rise. Traditional diagnostic biomarkers employed in clinical settings for MI diagnosis have various drawbacks, prompting researchers to investigate fast, precise, and highly sensitive biosensor platforms and technologies. Biosensors are analytical devices that combine biological elements with physicochemical transducers to detect and quantify specific compounds or analytes. These devices play a crucial role in various fields including healthcare, environmental monitoring, food safety, and biotechnology. Biosensors developed for the detection of cardiac biomarkers are typically electrochemical, mass, and optical biosensors. Nanomaterials have emerged as revolutionary components in the field of biosensing, offering unique properties that significantly enhance the sensitivity and specificity of the detection systems. This review provides a comprehensive overview of the advancements and applications of nanomaterial-based biosensing systems. Beginning with an exploration of the fundamental principles governing nanomaterials, we delve into their diverse properties, including but not limited to electrical, optical, magnetic, and thermal characteristics. The integration of these nanomaterials as transducers in biosensors has paved the way for unprecedented developments in analytical techniques. Moreover, the principles and types of biosensors and their applications in cardiovascular disease diagnosis are explained in detail. The current biosensors for cardiac biomarker detection are also discussed, with an elaboration of the pros and cons of existing platforms and concluding with future perspectives.

Plasmonic Fluorescence Enhancement in Diagnostics for Clinical Tests at Point-of-Care: A Review of Recent Technologies

Fluorescence-based biosensors have widely been used in the life-sciences and biomedical applications due to their low limit of detection and a diverse selection of fluorophores that enable simultaneous measurements of multiple biomarkers. Recent research effort has been made to implement fluorescent biosensors into the exploding field of point-of-care testing (POCT), which uses cost-effective strategies for rapid and affordable diagnostic testing. However, fluorescence-based assays often suffer from their feeble signal at low analyte concentrations, which often requires sophisticated, costly, and bulky instrumentation to maintain high detection sensitivity. Metal- and metal oxide-based nanostructures offer a simple solution to increase the output signal from fluorescent biosensors due to the generation of high field enhancements close to a metal or metal oxide surface, which has been shown to improve the excitation rate, quantum yield, photostability, and radiation pattern of fluorophores. This article provides an overview of existing biosensors that employ various strategies for fluorescence enhancement via nanostructures and have demonstrated the potential for use as POCT. Biosensors using nanostructures such as planar substrates, freestanding nanoparticles, and metal-dielectric-metal nanocavities are discussed with an emphasis placed on technologies that have shown promise towards POCT applications without the need for centralized laboratories.

GLAD Based Advanced Nanostructures for Diversified Biosensing Applications: Recent Progress

Glancing angle deposition (GLAD) is a technique for the fabrication of sculpted micro- and nanostructures under the conditions of oblique vapor flux incident and limited adatom diffusion. GLAD-based nanostructures are emerging platforms with broad sensing applications due to their high sensitivity, enhanced optical and catalytic properties, periodicity, and controlled morphology. GLAD-fabricated nanochips and substrates for chemical and biosensing applications are replacing conventionally used nanomaterials due to their broad scope, ease of fabrication, controlled growth parameters, and hence, sensing abilities. This review focuses on recent advances in the diverse nanostructures fabricated via GLAD and their applications in the biomedical field. The effects of morphology and deposition conditions on GLAD structures, their biosensing capability, and the use of these nanostructures for various biosensing applications such as surface plasmon resonance (SPR), fluorescence, surface-enhanced Raman spectroscopy (SERS), and colorimetric- and wettability-based bio-detection will be discussed in detail. GLAD has also found diverse applications in the case of molecular imaging techniques such as fluorescence, super-resolution, and photoacoustic imaging. In addition, some in vivo applications, such as drug delivery, have been discussed. Furthermore, we will also provide an overview of the status of GLAD technology as well as future challenges associated with GLAD-based nanostructures in the mentioned areas.

Fabrication and Characterization of Acute Myocardial Infarction Myoglobin Biomarker Based on Chromium-Doped Zinc Oxide Nanoparticles

In this article, we describe the fabrication and characterization of a sensor for acute myocardial infarction that detects myoglobin biomarkers using chromium (Cr)-doped zinc oxide (ZnO) nanoparticles (NPs). Pure and Cr-doped ZnO NPs (13 × 10¹⁷, 20 × 10¹⁷, and 32 × 10¹⁷ atoms/cm³ in the solid phase) were synthesized by a facile low-temperature sol-gel method. Synthesized NPs were examined for structure and morphological analysis using various techniques to confirm the successful formation of ZnO NPs. Zeta potential was measured in LB media at a negative value and increased with doping. XPS spectra confirmed the presence of oxygen deficiency in the synthesized material. To fabricate the sensor, synthesized NPs were screen-printed over a pre-fabricated gold-coated working electrode for electrochemical detection of myoglobin (Mb). Cr-doped ZnO NPs doped with 13 × 10¹⁷ Cr atomic/cm³ revealed the highest sensitivity of ~37.97 μA.cm⁻²nM⁻¹ and limit of detection (LOD) of 0.15 nM for Mb with a response time of ≤10 ms. The interference study was carried out with cytochrome c (Cyt-c) due to its resemblance with Mb and human serum albumin (HSA) abundance in the blood and displayed distinct oxidation potential and current values for Mb. Cr-doped ZnO NP-based Mb biosensors showed 3 times higher sensitivity as compared to pure ZnO NP-based sensors.

Electroanalysis of Biomolecules: Rational Selection of Sensor Construction

Methods of electrochemical analysis of biological objects based on the reaction of electro-oxidation/electro-reduction of molecules are presented. Polymer nanocomposite materials that modify electrodes to increase sensitivity of electrochemical events on the surface of electrodes are described. Examples of applications electrochemical biosensors constructed with nanocomposite material for detection of biological molecules are presented, advantages and drawbacks of different applications are discussed.

Review: Applications of surface-enhanced fluorescence (SEF) spectroscopy in bio-detection and biosensing

Surface-enhanced fluorescence (SEF) is rapidly becoming one of the main spectroscopic techniques for the detection of a variety of biomolecules and biomarkers. The main reasons for this trend are the high sensitivity and selectivity, robustness, and speed of this analytical method. Each year, the number of applications that utilize this phenomenon increases and with each such work, the complexity and novelty of the used substrates, procedures, and analytes rises. To obtain a clearer view of this phenomenon and research area, we decided to combine 76 valuable research articles from a variety of different research groups into this mini-review. We present and describe these works concisely and clearly, with a particular interest in the quantitative parameters of the experiment. These sources are classified according to the nature of the analyte, on the contrary to most reviews, which sort them by substrate nature. This point of view gives us insight into the development of this research area and the consequent increase in the complexity of the analyte nature. Moreover, this type of sorting can show possible future routes for the expansion of this research area. Along with the analytes, we can also pay attention to the substrates used for each situation and how the development of substrates affects the direction of research and subsequently, the choice of an analyte. About 108 sources and several interesting trends in the SEF research area over the past 25 years are discussed in this mini-review.

Staining Traditional Colloidal Gold Test Strips with Pt Nanoshell Enables Quantitative Point-of-Care Testing with Simple and Portable Pressure Meter Readout

Traditional immunochromatographic test strips based on colloidal gold are effective devices for portable and low-cost point-of-care (POC) testing. Nevertheless, they still suffer from the limitation of qualitative or semiquantitative tests via naked-eye detection. Replacement of gold with other signal entities, such as magnetic particles or fluorescent particles, requires professional instrumentation to obtain quantitative results. A pressure-based assay with platinum nanoparticles (PtNPs) can provide quantitative results using a portable pressure meter but is also hampered by the long-term instability of PtNPs. Consequently, we developed a Pt-staining method based on test strips to create platinum nanoshells on the surface of colloidal gold. This method not only preserves the original advantages of colloidal gold with easy synthesis and decoration but also introduces PtNPs with excellent catalytic activity as signal labels to achieve sensitive quantitative detection. Myoglobin was tested as a model target, and the limit of detection was 5.47 ng/mL in 20% diluted serum samples, which satisfies the requirements for clinical monitoring of acute myocardial infarction. In addition, the two most common colloidal gold strips available in the marketplace were applied to demonstrate the compatibility of Pt-staining. Taking advantage of low cost, user-friendliness, compatibility, simplicity, and stability, colloidal gold test strips with Pt-staining are expected to satisfy the need for quantitative POC testing of biomarkers, especially in resource-limited regions.

Centrifugal micropipette-tip with pressure signal readout for portable quantitative detection of myoglobin

Integration of a centrifugal micropipette-tip for sample processing and a pressure meter for quantitative readout enables portable detection of disease biomarkers.

Robust nanoplasmonic substrates for aptamer macroarrays with single-step detection of PDGF-BB

An aptamer macroarray on a robust nanoplasmonic substrate with fluorescence enhancement is developed for a single-step sensitive detection of human platelet-derived growth factor-BB (PDGF-BB), a predominant cancer biomarker in cancer angiogenesis. A hybrid Au-nanoparticles-poly (dimethylsiloxane) (PDMS) as nanoplasmonic substrate is prepared via the in-situ reduction of AuCl4(-) ions in PDMS matrixes onto 96 or 384 well plates. In the absence of target molecules, unfolded PDGF-BB aptamer conjugated with dye TAMRA is electrostatically bound to a positively charged poly-L-lysine (PLL)-coated Au nanocomposites film surface, and the fluorescence enhancement effects can be optimized by varying the distance between TAMRA and the Au nanocomposites film, which is easily adjusted by varying the thickness of the biocompatible poly-(acrylic acid) (PAA/PLL) multilayers, and thus metal-enhanced fluorescence of dye TAMRA conjugated with the aptamer is generated up to 15.2-fold. The interaction of the aptamer to its target induces the reversible conformation change of the aptamer, and consequently, the electrostatic potential is overcome by binding force. As a result, the target-binding interaction of the aptamer causes the irreversible detachment of the aptamer from the nanostructured Au film surface to decrease fluorescence of TAMRA. The aptamer macroarray provides not only the appropriate sensitivity for clinical diagnostics with a wide range of linear detection from 10pg/mL to 10μg/mL, high specificity for PDGF-BB against VEGF-165, VEGF-121, NaCl and IgG, and temporal biological stability, but also a single-step detection. We envision that the efficient and robust aptamer macroarray can be extended to the detection of other biomarkers.

Aptamers-based sandwich assay for silver-enhanced fluorescence multiplex detection

In this work, aptamers-modified silver nanoparticles (AgNPs) were prepared as capture substrate, and fluorescent dyes-modified aptamers were synthesized as detection probes. The sandwich assay was based on dual aptamers, which was aimed to accomplish the highly sensitive detection of single protein and multiplex detection of proteins on one-spot. We found that aptamers-modified AgNPs based microarray was much superior to the aptamer based microarray in fluorescence detection of proteins. The result shows that the detection limit of the sandwich assay using AgNPs probes for thrombin or platelet-derived growth factor-BB (PDGF-BB) is 80 or 8 times lower than that of aptamers used directly. For multiplex detection of proteins, the detection limit was 625 pM for PDGF-BB and 21 pM for thrombin respectively. The sandwich assay based on dual aptamers and AgNPs was sensitive and specific.

No Added Value of Novel Biomarkers in the Diagnostic Assessment of Patients Suspected of Acute Coronary Syndrome

BACKGROUND

Despite the availability of high-sensitive troponin (hs-cTnT), there is still room for improvement in the diagnostic assessment of patients suspected of acute coronary syndrome (ACS). Apart from serial biomarker testing, which is time-consuming, novel biomarkers like copeptin have been proposed to expedite the early diagnosis of suspected ACS in addition to hs-cTnT. We determined whether placenta derived growth factor (PlGF), soluble Fms-like tyrosine kinase 1 (sFlt-1), myoglobin, N-terminal prohormone B-type Natriuretic Peptide (NT-proBNP), growth-differentiation factor 15 (GDF-15) and copeptin improved early assessment of chest pain patients.

METHODS

This prospective, single centre diagnostic FAME-ER study included patients presenting to the ED with symptoms suggestive of ACS. Blood was collected to measure biomarkers, notably, hs-cTnT was retrospectively assessed. Added value of markers was judged by increase in AUC using multivariable logistic regression.

RESULTS

Of 453 patients enrolled, 149 (33%) received a final diagnosis of ACS. Hs-cTnT had the highest diagnostic value in both univariable and multivariable analysis. PPVs of the biomarkers ranged from 23.5% (PlGF) to 77.9% (hs-cTnT), NPVs from 67.0% (PlGF) to 86.4% (hs-cTnT). Only myoglobin yielded diagnostic value in addition to clinical symptoms and electrocardiography (ECG) (AUC of clinical model 0.80) with AUC of 0.84 (p<0.001). However, addition of hs-cTnT was superior (AUC 0.89, p<0.001). Addition of the biomarkers to our clinical model and hs-cTnT did not or only marginally (GDF-15) improved diagnostic performance.

CONCLUSION

When assessing patients suspected of ACS, only myoglobin had added diagnostic value beyond clinical symptoms and ECG. However, when combined with hs-cTnT, it yields no additional diagnostic value. PlGF, sFlt-1, NT-proBNP, GDF-15 and copeptin had no added value to the clinical model or hs-cTnT.

Amplification of the signal intensity of fluorescence-based fiber-optic biosensors using a Fabry-Perot resonator structure

Fluorescent biosensors have been widely used in biomedical applications. To amplify the intensity of fluorescence signals, this study developed a novel structure for an evanescent wave fiber-optic biosensor by using a Fabry-Perot resonator structure. An excitation light was coupled into the optical fiber through a laser-drilled hole on the proximal end of the resonator. After entering the resonator, the excitation light was reflected back and forth inside the resonator, thereby amplifying the intensity of the light in the fiber. Subsequently, the light was used to excite the fluorescent molecules in the reactive region of the sensor. The experimental results showed that the biosensor signal was amplified eight-fold when the resonator reflector was formed using a 92% reflective coating. Furthermore, in a simulation, the biosensor signal could be amplified 20-fold by using a 99% reflector.

Plasmon-Enhanced Fluorescence Biosensors: a Review

Surfaces of metallic films and metallic nanoparticles can strongly confine electromagnetic field through its coupling to propagating or localized surface plasmons. This interaction is associated with large enhancement of the field intensity and local optical density of states which provides means to increase excitation rate, raise quantum yield, and control far field angular distribution of fluorescence light emitted by organic dyes and quantum dots. Such emitters are commonly used as labels in assays for detection of chemical and biological species. Their interaction with surface plasmons allows amplifying fluorescence signal (brightness) that accompanies molecular binding events by several orders of magnitude. In conjunction with interfacial architectures for the specific capture of target analyte on a metallic surface, plasmon-enhanced fluorescence (PEF) that is also referred to as metal-enhanced fluorescence (MEF) represents an attractive method for shortening detection times and increasing sensitivity of various fluorescence-based analytical technologies. This review provides an introduction to fundamentals of PEF, illustrates current developments in design of metallic nanostructures for efficient fluorescence signal amplification that utilizes propagating and localized surface plasmons, and summarizes current implementations to biosensors for detection of trace amounts of biomarkers, toxins, and pathogens that are relevant to medical diagnostics and food control.

Bio-functionalized Pt nanoparticles based electrochemical impedance immunosensor for human cardiac myoglobin

We report the covalent immobilization of three-dimensional carboxyl-functionalized Pt(MPA) nanoparticles with myoglobin protein antibody by carbodiimide coupling reaction deposited onto an indium-tin-oxide-coated glass plate for the construction of a bioelectrode.

Microstructural and electrochemical impedance characterization of bio-functionalized ultrafine ZnS nanocrystals-reduced graphene oxide hybrid for immunosensor applications

We report a mercaptopropionic acid capped ZnS nanocrystals decorated reduced graphene oxide (RGO) hybrid film on a silane modified indium-tin-oxide glass plate, as a bioelectrode for the quantitative detection of human cardiac myoglobin (Ag-cMb). The ZnS nanocrystals were anchored over electrochemically reduced GO sheets through a cross linker, 1-pyrenemethylamine hydrochloride, by carbodiimide reaction and have been characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The transmission electron microscopic characterization of the ZnS-RGO hybrid shows the uniform distribution of ultra-fine nanoparticles of ZnS in nano-sheets of GO throughout the material. The protein antibody, Ab-cMb, was covalently linked to ZnS-RGO nanocomposite hybrid for the fabrication of the bioelectrode. A detailed electrochemical immunosensing study has been carried out on the bioelectrode towards the detection of target Ag-cMb. The optimal fitted equivalent circuit model that matches the impedance response has been studied to delineate the biocompatibility, sensitivity and selectivity of the bioelectrode. The bioelectrode exhibited a linear electrochemical impedance response to Ag-cMb in a range of 10 ng to 1 μg mL(-1) in PBS (pH 7.4) with a sensitivity of 177.56 Ω cm(2) per decade. The combined synergistic effects of the high surface-to-volume ratio of ZnS(MPA) nanocrystals and conducting RGO has provided a dominant charge transfer characteristic (R(et)) at the lower frequency region of <10 Hz showing a good biocompatibility and enhanced impedance sensitivity towards target Ag-cMb. The impedance response sensitivity of the ZnS-RGO hybrid bioelectrode towards Ag-cMb has been found to be about 2.5 fold higher than that of a bare RGO modified bioelectrode.

[Electrochemical sensor systems based on one dimensional (1D) nanostructures for analysis of bioaffinity interactions]

It was shown that modification of screen printed graphite electrodes with gold nanoparticles (AuNPs) decorated Pb nanowires (PbNWs) demonstrates the enhancement of sensor's analytical characteristics such as effective surface area, electro catalytic properties and heterogeneous electron transfer kinetics. The reason for such improvement may be the synergistic effect ofAuNPs and PbNWs. Nanowires ensembles on electrode surface were employed for the detection of hemeproteins cytochrome P450 2B4, cytochrome c, and cardiac myoglobin in human plasma. Composite materials based on nanoparticles with different dimentions (3D three dimensional gold nanoparticles and 1D one dimensional Pb nanowires make it possible to construct biosensors with low detection limit of proteins.

A straightforward immunoassay applicable to a wide range of antibodies based on surface enhanced fluorescence

A straightforward immunoassay based on surface enhanced fluorescence (SEF) has been demonstrated using a fluorescent immune substrate and antibody functionalized-silver nanoparticles. Unlike the conventional SEF-based immunoassay, which usually uses the dye-labeled antibodies and the metallic nanostructured-substrates, the presented immune system does not need the antibodies to be labeled with dye molecules. Thus, this immunoassay can be easily applied to the detection of a wide range of target antigens, which is of great importance for its practical application. The experimental results show that this immunoassay has a good specificity as well as the capacity of quantitative detection. Basically, the surface density of the immuno-adsorbed silver nanoparticles increases with the increased amount of target antigens, resulting in a fluorescence enhancement up to around 7 fold. The dose-responsive performance of the immunoassay has been investigated and the limit of detection (LOD) is 1 ng/mL. Due to its simple preparation method and the wide range of detectable antigens, this presented immunoassay is expected to be helpful for extending the SEF-based application.

Registration of the protein with compact disk

CD-based optico-acoustical biosensor (OAB) was used for detection of various types of proteins represented by bovine serum albumin (BSA), heme-containing myoglobin (Mb), monoclonal antibody against viral protein marker of hepatitis B (anti-HBsAg) and membrane-bound cytochrome P450scc (P450scc). We applied standard compact disc reader (CD-ROM) as an optical analyzer and a standard compact disc (CD) as a biochip containing immobilized protein molecules. This biosensor can translate into a digital code the changes of optical signal from the proteins and their complexes immobilized on the CD surface. Then, the digital code is translated into an acoustic series or, in other words, into a "music of proteins". We demonstrate the use of the OAB for direct detection of proteins with different molecular weights, such as BSA, Mb, P450scc, anti-HBsAg with the concentration detection limit (DL) about 10(-7)M. By signal amplification achieved with autometallography, a higher sensitivity level (DL∼10(-9)M) for the detection of myoglobin was obtained. The method of OAB-detection of proteins is cheap: it requires no special equipment like spectrometers, refractometers and other devices. Due to the fact that acoustic series of the protein complexes antigen/antibody differs from that of single proteins, the OAB-detection is of particular interest for rapid assay in yes/no data type and for home diagnostics. Combination of the OAB with a mass spectrometer allowed the detection and identification of the target proteins fished out directly onto a standard CD surface.

MS-based ligand binding assays with speed, sensitivity, and specificity

Immunoassays are widely used in biochemical/clinical laboratories owing to their simplicity, speed, and sensitivity. We combined self-assembled monolayer-based immunoassays with MALDI-TOF MS to show that high-fidelity surface preparations with a novel matrix deposition/crystallization technique permits quantitative analysis of monolayer-bound antigens at picomolar detection limits. Calibration curves for intact proteins are possible over a broad concentration range and improved specificity of MS-immunoassays is highlighted by simultaneous label-free quantitation of ligand-bound protein complexes.

Enhancement of immunoassay's fluorescence and detection sensitivity using three-dimensional plasmonic nano-antenna-dots array

Protein detection is universal and vital in biological study and medical diagnosis (e.g., cancer detection). Fluorescent immunoassay is one of the most widely used and most sensitive methods in protein detection (Giljohann, D. A.; Mirkin, C. A. Nature2009, 462, 461-464; Yager, P.; et al. Nature2006, 442, 412-418). Improvements of such assays have many significant implications. Here, we report the use of a new plasmonic structure and a molecular spacer to enhance the average fluorescence of an immunoassay of Protein A and human immunoglobulin G (IgG) by over 7400-fold and the immunoassay's detection sensitivity by 3,000,000-fold (the limit of detection is reduced from 0.9 × 10(-9) to 0.3 × 10(-15) molar (i.e., from 0.9 nM to 300 aM), compared to identical assays performed on glass plates). Furthermore, the average fluorescence enhancement has a dynamic range of 8 orders of magnitude and is uniform over the entire large sample area with a spatial variation ±9%. Additionally, we observed that, when a single molecule fluorophore is placed at a "hot spot" of the plasmonic structure, its fluorescence is enhanced by 4 × 10(6)-fold, thus indicating the potential to further significantly increase the average fluorescence enhancement and the detection sensitivity. Together with good spatial uniformity, wide dynamic range, and ease to manufacture, the giant enhancement in immunoassay's fluorescence and detection sensitivity (orders of magnitude higher than previously reported) should open up broad applications in biology study, medical diagnosis, and others.

Plasmonic substrates for multiplexed protein microarrays with femtomolar sensitivity and broad dynamic range

Protein chips are widely used for high-throughput proteomic analysis, but to date, the low sensitivity and narrow dynamic range have limited their capabilities in diagnostics and proteomics. Here we present protein microarrays on a novel nanostructured, plasmonic gold film with near-infrared fluorescence enhancement of up to 100-fold, extending the dynamic range of protein detection by three orders of magnitude towards the fM regime. We employ plasmonic protein microarrays for the early detection of a cancer biomarker, carcinoembryonic antigen, in the sera of mice bearing a xenograft tumour model. Further, we demonstrate a multiplexed autoantigen array for human autoantibodies implicated in a range of autoimmune diseases with superior signal-to-noise ratios and broader dynamic range compared with commercial nitrocellulose and glass substrates. The high sensitivity, broad dynamic range and easy adaptability of plasmonic protein chips presents new opportunities in proteomic research and diagnostics applications.

[Sensor systems for medical application based on hemoproteins and nanocomposite materials]

Recent advances in nanotechnologies stimulate the development of sensor systems based on nanocomposite materials. This review discusses the prospects and challenges of sensors coupled with functionally important for medicine hemoproteins and nanoscale materials. Authors summarized their own experimental results and literature data on hemoprotein-based sensor systems. Mechanisms and the main function principles of electrochemical nanosensors are also discussed.

Improved detectability and signal strength for rotating phase fluorescence immunoassays through image processing

Fluorescence immunoassays based on rotating solid phase have shown promise of lowered detection limits, among other advantages. However, intrinsic background distortion effects have limited their utility. Here, novel image processing strategies are used to minimize these effects and improve the estimate of concentration and lower the detection limit. This initial demonstration of a new processing capability is performed on data for a protein, myoglobin, which is a biomarker for acute myocardial infarction. For these data, compared with published results, the detection limit is improved by a factor of approximately one hundred (to 700 fM), which is competitive with or better than other immunoassay strategies (ELISA, for example) that are fully developed. This work suggests that image and video processing technologies can provide a valuable alternative approach to biochemical detection and concentration estimation.

Quantitative Comparison of Protein Surface Coverage on Glass Slides and Silver Island Films in Metal-Enhanced Fluorescence-based Biosensing Applications

The use of Metal-Enhanced Fluorescence (MEF) phenomenon in fluorescence-based bioassays affords for increased sensitivity to be realized by incorporating metal nanoparticles onto planar surfaces. The close-range interactions of metal-fluorophores result in increased fluorescence emission from the bioassays, which in turn affords for the detection of target biomolecules at lower concentrations. Moreover, the use of silver nanoparticles increases the photostability of fluorophores improving the detectability of fluorescence emission under prolonged use of excitation light. Although numerous reports on MEF-based biosensing applications exist, the contribution of protein coverage on Silver Island Films (SIFs) on the increased fluorescence emission was never investigated. This work presents our findings on the quantitative comparison of protein surface coverage on SIFs and blank glass slides. In this regard, identical protein bioassay for a model protein (biotinylated bovine serum albumin, b-BSA) on these surfaces is constructed and the relative extent of protein surface coverage on SIFs and blank glass slides was determined using radio-labeled biomolecules. It was found that the total scintillation counts on SIFs and blank glass slides were similar for BSA concentrations ranging from 1 μM to 1 pM, which implies that increased fluorescence in MEF-based biosensing applications is only due to metal-fluorophore interactions.

Electrochemical immunoanalysis of cardiac myoglobin

Method targeting the direct monitoring of myoglobin based on analysis of electrochemical parameters of modified electrodes were proposed. Method of direct detection is based on interaction of myoglobin with anti-myoglobin with subsequent electrochemical registration of hemeprotien. Myocardial infarction biomarker myoglobin was quantified at biological level using screen printed electrodes modified with gold nanoparticles stabilized with didodecyldimethylammonium bromide (DDAB) and antibodies. Proposed method did not require signal enhancement and amplification and also labeled secondary antibodies. Electro analysis has high specificity and sensitivity. Myoglobin -antibodies interaction was studied also with electrochemical impedance spectroscopy. Sensor has low detection limit and broad diapason of working concentrations (17.8 ng/ml - 1780 ng/ml; 1 nM - 10 nM). Method based on gold nanoparticles detection on the surface of electrodes was treated for myoglobin identification. AuNP worked as an electrochemical sensing platform: the oxidation of gold surface (resulted in gold oxide formation) upon polarization served as a basis for analytical response. The difference of cathodic peak area and peak high of gold oxide reduction in the case of electrodes with antibodies and electrodes with antibodies - myoglobin complex, was registered.

Electrochemical nanobiosensor for express diagnosis of acute myocardial infarction in undiluted plasma

The myocardial infarction biomarker myoglobin was quantified at the biological level in undiluted plasma using developed electrochemical nanosensors with immobilized anti-myoglobin. Method for cardiac myoglobin detection is based on direct electron transfer between Fe(III)-heme and electrode surface modified with gold nanoparticles/didodecyldimethylammonium bromide (DDAB/Au) and antibodies. The procedure of myoglobin detection was optimized (pH, incubation times and characteristics of electrodes) to express determination of the marker in serum or plasma. Plasma of healthy donors and patients with acute myocardial infarction (AMI) was analyzed using electrochemical immunosensors and RAMP immunoassay. Square wave voltammetry cathodic peak of cardiac myoglobin reduction was found to be proportional to myoglobin quantity in plasma as determined by RAMP. The method proposed does not require signal enhancement or amplification; nor does it require labeled secondary antibodies. Immunosensor has a detection limit of 10 ng/ml (0.56 nM) and a broad range of working concentrations (10-1780 ng/ml; 0.56-100 nM). The whole procedure takes 30 min and can be used for express diagnosis of acute myocardial infarction.

Nanostructured silver-based surfaces: new emergent methodologies for an easy detection of analytes

In this work, we describe how to realize a new sensing platform for an easy and fast detection of analytes. In particular, we utilized enhanced fluorescence emission on silver island films (SIFs) coupled to the total internal reflection fluorescence mode (TIRF) to develop a new assay format for the detection of target analytes. Here, as an example, we report on the detection of the toxic peptides present in gliadin (Gli). Our assay was performed as follows: (1) gliadin was first captured on surfaces coated with anti-Gli antibodies; (2) the surfaces were then incubated with fluorophore-labeled anti-Gli antibodies; (3) the signal from the fluorophore-labeled anti-Gli antibody bound to the antigen was detected by TIRF. The system was examined on glass surfaces and on SIFs. We observed a relevant enhancement of the signal from SIFs compared to the signal from the glass substrate not modified with a SIF. In addition, the estimated detection limit (EDL) of our methodology was 60 ng/mL (or lower). This limit is therefore lower than the clinical cut-off for Gli presence in food for celiac patients. The advantage of our method is a reduced number of testing steps, which allows for easy detection of residual toxic peptides in food labeled as gluten free. The proposed technology can be easily expanded to the determination of different target analytes.

Nanoparticle strategies for enhancing the sensitivity of fluorescence-based biochips

This article describes strategies for achieving fluorescence enhancement in optical biochips. Two strategies are discussed: plasmonic enhancement, which is due to the localized surface plasmon resonance of metal nanostructures that are adjacent to the fluorescent labels in optical immunoassays; and the use of high-brightness silica nanoparticles as enhanced labels. We present a review of the state-of-the-art in both areas, including synthesis techniques for the metal and silica nanoparticles and the use of the nanoparticles in optical immunoassays. Data are presented that highlight the key design parameters which influence the level of enhancement and model assay data are presented that illustrate potential enhancements in assay performance.

Superparamagnetic microsphere-assisted fluoroimmunoassay for rapid assessment of acute myocardial infarction

Rapid assessment of acute myocardial infarction (AMI) was successfully demonstrated using an improved superparamagnetic polymer microsphere-assisted sandwich fluoroimmunoassay to detect two early cardiac markers-myoglobin and human heart-type fatty acid binding protein (H-FABP). This assay used a preparation of superparamagnetic poly(styrene-divinylbenzene-acrylamide) microspheres, glutaraldehyde-coupled capture antibodies (monoclonal anti-myoglobin 7C3 and anti-H-FABP 10E1) grafted onto the polymer microspheres, and a sequential sandwich fluoroimmunoassay using detection antibodies (FITC-labeled anti-myoglobin 4E2 and FITC-labeled anti-H-FABP 9F3). Characterization of the polymer microspheres by TEM, SEM and Fourier transform infrared spectroscopy (FT-IR) showed that the microspheres were uniformly round with an average diameter of 1.12 microm, and had a Fe(3)O(4)-polymer core-shell structure (shell thickness was about 84 nm) with 0.22 mmol/g amino groups on their surfaces. The magnetic behavior of the Fe(3)O(4)-polymer microspheres was superparamagnetic (M(s)=13 emu/g, H(c)=13.1 Oe). Fluorescence images of the post-immunoassay microspheres recorded using a confocal laser-scanning microscope showed that the average fluorescence intensity was correlated with the concentration of cardiac markers, in agreement with the results obtained by an F-4500 FL spectrophotometer; this indicated that the fluoroimmunoassay could be used to semi-quantitatively detect both myoglobin and H-FABP. The detection limit was 25 ng/mL for myoglobin and 1 ng/mL for H-FABP.

A microemulsion preparation of nanoparticles of europium in silica with luminescence enhancement using silver

A facile one-pot microemulsion method has been developed for the synthesis of spherical silver core-silica shell (Ag@SiO2) nanoparticles with europium chelates doped in the shell through a silane agent. The method is significantly more straightforward than other extant methods. Measurements of the luminescent emissions from the Ag@SiO2 nanoparticles, in comparison with control silica nanoparticles without silver cores, showed that the presence of the silver cores can increase the fluorescence intensity approximately 24-fold and decrease the luminescence lifetime. This enhancement offers a potential increase in overall particle detectability with increased fluorophore photostability.

Nanomaterials in fluorescence-based biosensing

Fluorescence-based detection is the most common method utilized in biosensing because of its high sensitivity, simplicity, and diversity. In the era of nanotechnology, nanomaterials are starting to replace traditional organic dyes as detection labels because they offer superior optical properties, such as brighter fluorescence, wider selections of excitation and emission wavelengths, higher photostability, etc. Their size- or shape-controllable optical characteristics also facilitate the selection of diverse probes for higher assay throughput. Furthermore, the nanostructure can provide a solid support for sensing assays with multiple probe molecules attached to each nanostructure, simplifying assay design and increasing the labeling ratio for higher sensitivity. The current review summarizes the applications of nanomaterials--including quantum dots, metal nanoparticles, and silica nanoparticles--in biosensing using detection techniques such as fluorescence, fluorescence resonance energy transfer (FRET), fluorescence lifetime measurement, and multiphoton microscopy. The advantages nanomaterials bring to the field of biosensing are discussed. The review also points out the importance of analytical separations in the preparation of nanomaterials with fine optical and physical properties for biosensing. In conclusion, nanotechnology provides a great opportunity to analytical chemists to develop better sensing strategies, but also relies on modern analytical techniques to pave its way to practical applications.

Near-infrared squaraine dyes for fluorescence enhanced surface assay

Commercially available, near-infrared fluorescent squaraine dyes (Seta-635 and Seta-670) were covalently bound to antibodies and employed insurface enhanced immunoassay. From fluorescence intensity and lifetime changes determined for a surface which had been coated with silver nanoparticles as well as a non-coated glass surface, both labelled compounds exhibited a 15 to 20-fold enhancement of fluorescence on the silver coated surface compared to that achieved on the non-coated surface. In addition, the fluorescence lifetime changes drastically for both labels in the case of silver-coated surfaces. The fluorescence signal enhancement obtained for the two dyes was greater than that previously recorded for Rhodamine Red-X and AlexaFluor-647 labels.