Microcavity-based SERS chip for ultrasensitive immune detection of cardiac biomarkers

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.

Immunoassays: Analytical and Clinical Performance, Challenges, and Perspectives of SERS Detection in Comparison with Fluorescent Spectroscopic Detection

Immunoassays (IAs) with fluorescence-based detection are already well-established commercialized biosensing methods, such as enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (LFIA). Immunoassays with surface-enhanced Raman spectroscopy (SERS) detection have received significant attention from the research community for at least two decades, but so far they still lack a wide clinical commercial application. This review, unlike any other review that we have seen, performs a three-dimensional performance comparison of SERS IAs vs. fluorescence IAs. First, we compared the limit of detection (LOD) as a key performance parameter for 30 fluorescence and 30 SERS-based immunoassays reported in the literature. We also compared the clinical performances of a smaller number of available reports for SERS vs. fluorescence immunoassays (FIAs). We found that the median and geometric average LODs are about 1.5-2 orders of magnitude lower for SERS-based immunoassays in comparison to fluorescence-based immunoassays. For instance, the median LOD for SERS IA is 4.3 × 10-13 M, whereas for FIA, it is 1.5 × 10-11 M. However, there is no significant difference in average relative standard deviation (RSD)-both are about 5-6%. The analysis of sensitivity, selectivity, and accuracy reported for a limited number of the published clinical studies with SERS IA and FIA demonstrates an advantage of SERS IA over FIA, at least in terms of the median value for all three of those parameters. We discussed common and specific challenges to the performances of both SERS IA and FIA, while proposing some solutions to mitigate those challenges for both techniques. These challenges include non-specific protein binding, non-specific interactions in the immunoassays, sometimes insufficient reproducibility, relatively long assay times, photobleaching, etc. Overall, this review may be useful for a large number of researchers who would like to use immunoassays, but particularly for those who would like to make improvements and move forward in both SERS-based IAs and fluorescence-based IAs.

A SERS substrate based on perovskite quantum dots and graphene for the determination of cardiac troponin I

Noble metal has always been used as a preferred base for SERS substrate. However, the preparation cost of such materials is trully high. Therefore, many researchers have begun to search for succedanea which cost were lower. In this work, CsPbBr3@ZIF-8 was synthesized by in-situ reduction method and combined with graphene nanosheets to construct a SERS substrate. The SERS performance of this substrate could be further enhanced by the synergistic effect of perovskite quantum dots and graphene. Base on this material, a sensitive SERS strategy composed of CsPbBr3@ZIF-8@G, antibody, and Bradford method was developed for the quantitative determination of cardiac troponin I (cTnI) in human serum. It's worth noting that the sensitivity and accuracy of this method could approach the level of other SERS methods using noble metals. The "reverse"-SERS method could improve the uniformity and stability of detection platform obviously. The detection range of this method was 0.01-100 ng/mL, and the estimated detection of limit (LOD) was 4.7 pg/mL. The recovery rate of this method range was between 93.1 % and 104.8 %, and RSD range was between 4.47 % and 7.06 %.

Progress in the Optical Sensing of Cardiac Biomarkers

Biomarkers play key roles in the diagnosis, risk assessment, treatment and supervision of cardiovascular diseases (CVD). Optical biosensors and assays are valuable analytical tools answering the need for fast and reliable measurements of biomarker levels. This review presents a survey of recent literature with a focus on the past 5 years. The data indicate continuing trends towards multiplexed, simpler, cheaper, faster and innovative sensing while newer tendencies concern minimizing the sample volume or using alternative sampling matrices such as saliva for less invasive assays. Utilizing the enzyme-mimicking activity of nanomaterials gained ground in comparison to their more traditional roles as signaling probes, immobilization supports for biomolecules and for signal amplification. The growing use of aptamers as replacements for antibodies prompted emerging applications of DNA amplification and editing techniques. Optical biosensors and assays were tested with larger sets of clinical samples and compared with the current standard methods. The ambitious goals on the horizon for CVD testing include the discovery and determination of relevant biomarkers with the help of artificial intelligence, more stable specific recognition elements for biomarkers and fast, cheap readers and disposable tests to facilitate rapid testing at home. As the field is progressing at an impressive pace, the opportunities for biosensors in the optical sensing of CVD biomarkers remain significant.

An anisotropic nanobox based core-shell-satellite nanoassembly of multiple SERS enhancement with heterogeneous interface for stroke marker determination

Herein, A novel gold-silver alloy nanobox (AuAgNB)@SiO₂-gold nanosphere (AuNP) nanoassembly based on core-shell-satellite structure is fabricated and applied to the surface-enhanced Raman scattering (SERS) detection of S100 calcium-binding protein B protein (S100B). It contains an anisotropic hollow porous AuAgNB core with rough surface, an ultrathin silica interlayer labeled with reporter molecules, and AuNP satellites. The nanoassemblies were systematically optimized by tuning the reporter molecules concentration, silica layer thickness, AuAgNB size, and the size and number of AuNP satellite size. Remarkably, AuNP satellites are adjacent to AuAgNB@SiO₂, developing AuAg-SiO₂-Au heterogeneous interface. With the strong plasmon coupling between AuAgNB and AuNP satellites, chemical enhancement from heterogeneous interface, and the tip "hot spots" of AuAgNB, the SERS activity of the nanoassemblies was multiply enhanced. Additionally, the stability of nanostructure and Raman signal was significantly improved by the silica interlayer and AuNP satellites. Eventually, the nanoassemblies were applied for S100B detection. It demonstrated satisfactory sensitivity and reproducibility with a wide detection range of 10 fg/mL-10 ng/mL and a limit of detection (LOD) of 1.7 fg/mL. This work based on the AuAgNB@SiO₂-AuNP nanoassemblies with multiple SERS enhancements and favorable stability demonstrates the promising application in stroke diagnosis.

The Convenience of Polydopamine in Designing SERS Biosensors with a Sustainable Prospect for Medical Application

Polydopamine (PDA) is a multifunctional biomimetic material that is friendly to biological organisms and the environment, and surface-enhanced Raman scattering (SERS) sensors have the potential to be reused. Inspired by these two factors, this review summarizes examples of PDA-modified materials at the micron or nanoscale to provide suggestions for designing intelligent and sustainable SERS biosensors that can quickly and accurately monitor disease progression. Undoubtedly, PDA is a kind of double-sided adhesive, introducing various desired metals, Raman signal molecules, recognition components, and diverse sensing platforms to enhance the sensitivity, specificity, repeatability, and practicality of SERS sensors. Particularly, core-shell and chain-like structures could be constructed by PDA facilely, and then combined with microfluidic chips, microarrays, and lateral flow assays to provide excellent references. In addition, PDA membranes with special patterns, and hydrophobic and strong mechanical properties can be used as independent platforms to carry SERS substances. As an organic semiconductor material capable of facilitating charge transfer, PDA may possess the potential for chemical enhancement in SERS. In-depth research on the properties of PDA will be helpful for the development of multi-mode sensing and the integration of diagnosis and treatment.

Recyclable detection of gefitinib in clinical sample mediated by multifunctional Ag-anchored g-C3N4/MoS2 composite substrate

Surface-enhanced Raman scattering (SERS) technology enables to satisfy the increasing demand of clinical drug monitoring due to the superiority of fingerprint recognition, real-time response, and nondestructive collection. Here, a novel graphitic carbon nitride (g-C₃N₄)/ molybdenum disulfide (MoS₂)/Ag composite substrate with a 3D surface structure was successfully developed for the recyclable detection of gefitinib in serum. Attributed to the uniform and dense "hotspots" on the shrubby active surfaces in conjunction with the potential synergistic chemical enhancement of g-C₃N₄/MoS₂ heterosystem, a remarkable SERS sensitivity with an attractive enhancement factor value of 3.3 × 10⁷ was demonstrated. Meanwhile, a type-II heterojunction between g-C₃N₄ and MoS₂ enabled more efficient diffusion of photogenerated e^--h⁺ pairs assisted by the localized surface plasmon resonance of Ag NPs, which contributed to the reliable recyclable detection of gefitinib. The ultra-low limit of detection at 10^-5 mg/mL and high recycling rates of gefitinib beyond 90% in serum were successfully realized. The results demonstrated the as-prepared SERS substrate has tremendous potential to be untilized for in-situ drug diagnostics.

SERS-Based Immunoassay of Myocardial Infarction Biomarkers on a Microfluidic Chip with Plasmonic Nanostripe Microcones

We developed a new plasmonic nanostripe microcone array (PNMA) substrate-integrated microfluidic chip for the simultaneous surface-enhanced Raman scattering (SERS)-based immunoassay of the creatine kinase MB isoenzyme (CK-MB) and cardiac troponin (cTnI) cardiac markers. The conventional immunoassay usually employs a microtiter plate as the solid capture plate to form the immunocomplexes. However, the two-dimensional (2D) surface of the microtiter plate limits the capture efficiency of the target antigens due to the steric hindrance effect. To address this issue, a gold film-coated microcone array with nanostripes was developed that can provide a large surface area for capture antibody conjugation and serve as a SERS-active substrate. This unique nano-microhierarchical structure showed an excellent light trapping effect and induced surface plasmon resonance to further enhance the Raman signals of the SERS nanoprobes. It significantly improved the sensitivity and applicability of SERS-based immunoassay on the microfluidic chip. With this integrated microfluidic chip, we successfully performed the simultaneous detection of CK-MB and cTnI, and the detection limit can reach 0.01 ng mL^-1. It is believed that the PNMA substrate-integrated microfluidic chip would play a critical role in the rapid and sensitive diagnostics of cardiac diseases.

A review of cardiac troponin I detection by surface enhanced Raman spectroscopy: Under the spotlight of point-of-care testing

Cardiac troponin I (cTnI) is a biomarker widely related to acute myocardial infarction (AMI), one of the leading causes of death around the world. Point-of-care testing (POCT) of cTnI not only demands a short turnaround time for its detection but the highest accuracy levels to set expeditious and adequate clinical decisions. The analytical technique Surface-enhanced Raman spectroscopy (SERS) possesses several properties that tailor to the POCT format, such as its flexibility to couple with rapid assay platforms like microfluidics and paper-based immunoassays. Here, we analyze the strategies used for the detection of cTnI by SERS considering POCT requirements. From the detection ranges reported in the reviewed literature, we suggest the diseases other than AMI that could be diagnosed with this technique. For this, a section with information about cardiac and non-cardiac diseases with cTnI release, including their release kinetics or cut-off values are presented. Likewise, POCT features, the use of SERS as a POCT technique, and the biochemistry of cTnI are discussed. The information provided in this review allowed the identification of strengths and lacks of the available SERS-based point-of-care tests for cTnI and the disclosing of requirements for future assays design.

A novel Apt-SERS platform for the determination of cardiac troponin I based on coral-like silver-modified magnetic substrate and BCA method

As a kind of acute cardiovascular disease, acute myocardial infarction (AMI) endangers human's life and fitness seriously. The detection of cardiac troponin I (cTnI), a biomarker of AMI, is the key to early medical prognosis and treatment. Surface-enhanced Raman spectroscopy is viewed to be an effective approach for detection of low-concentration substances, and aptamers are regarded to be effective fragments to recognize proteins specifically. In this work, a magnetic nanoparticle substrate coated with coral-like nano-silver was prepared, and the aptamer-modified substrate Fe₃O₄@PEI/Ag NC-Apt was used as magnetic capture probe. Combined with BCA method and SERS detection technology, an Apt-SERS platform was successfully constructed and used for high sensitivity quantitative detection of protein. Taking cTnI as the target, the detection range of the proposed Apt-SERS platform was 0.001-100 ng mL^-1, and the estimated detection of limit (LOD) was 0.23 pg mL^-1. The recovery and relative standard deviations (RSD) of spiked experiment in human serum samples were 92-106% and 3.8-10.1%, respectively. The platform combining BCA method and SERS provides a high sensitivity and good reproducibility method for cTnI detection, which offers a new method for the specific detection and analysis of proteins.

Metasurface Micro/Nano-Optical Sensors: Principles and Applications

Metasurfaces are 2D artificial materials consisting of arrays of metamolecules, which are exquisitely designed to manipulate light in terms of amplitude, phase, and polarization state with spatial resolutions at the subwavelength scale. Traditional micro/nano-optical sensors (MNOSs) pursue high sensitivity through strongly localized optical fields based on diffractive and refractive optics, microcavities, and interferometers. Although detections of ultra-low concentrations of analytes have already been demonstrated, the label-free sensing and recognition of complex and unknown samples remain challenging, requiring multiple readouts from sensors, e.g., refractive index, absorption/emission spectrum, chirality, etc. Additionally, the reliability of detecting large, inhomogeneous biosamples may be compromised by the limited near-field sensing area from the localization of light. Here, we review recent advances in metasurface-based MNOSs and compare them with counterparts using micro-optics from aspects of physics, working principles, and applications. By virtue of underlying the physics and design flexibilities of metasurfaces, MNOSs have now been endowed with superb performances and advanced functionalities, leading toward highly integrated smart sensing platforms.

Aptamer-modified magnetic SERS substrate for label-based determination of cardiac troponin I

A sensitive label-based SERS strategy composed of magnetic bimetallic nanoparticles Fe₃O₄@Ag@Au, specific aptamer, and Bradford method was developed for the quantitative determination of cardiac troponin I (cTnI) in human serum. The prepared substrate with high magnetic character, signal enhancement, and uniformity exhibited significant Raman response. After the substrate was bound to the aptamer, the target protein cTnI was specifically captured, and it showed the Raman signal when the signal reporter Coomassie Brilliant Blue G-250 (CBBG) was supplied. The Raman signal intensity at 1621 cm^-1 showed a wide linear relationship with the log value of the cTnI concentration in the range 0.01 to 100 ng·mL^-1, and the estimated limit of detection (LOD) was 5.50 pg·mL^-1. The recovery and relative standard deviation (RSD) of the spike experiment in human serum samples were 92-115% and 7.4-12.7%, respectively.