Nanohoneycomb Surface-Enhanced Raman Spectroscopy-Active Chip for the Determination of Biomarkers of Hepatocellular Carcinoma

Using signal off-to-on strategy for designing precise and ultrasensitive biosensor towards hepatocellular carcinoma through protein variant detection based on biocompatible bimetallic MOF

The high mortality rate of patients with hepatocellular carcinoma (HCC) is an ever-increasing worldwide concern. Fortunately, the newest research has found that the proportion of a protein variant in total alpha-fetoprotein (AFP) over 10 % can accurately predict the incidence of HCC. Therefore, a signal off-to-on strategy was designed for developing a novel precise and ultrasensitive biosensor towards HCC through protein variant detection based on bimetallic metal-organic framework (MOF). In this study, the biocompatible Fe2Ni-MOF was used as an electrochemically immobilized carrier, which provided abundant active sites and exhibited a synergistic effect between Fe and Ni ions for dramatically promoting the electron transfer and improving the electrochemical reduction efficiency, prominently facilitating signal amplification of the biosensing platform. Then, we designed a novel ordered labeling method to distinguish AFP-L3 from overall AFP and introduced a signal off-to-on strategy for achieving highly efficient determination of AFP-L3 %. This proposed biosensor demonstrated a satisfactory linear range, along with a very low detection limit of 69 pg/mL for AFP-L3, which was far below the medically relevant threshold level. Furthermore, the adopted biosensor presented preeminent specificity, and favorable reproducibility.

Targeted molecular rapid SERS diagnosis in clinical human serum through aptamer origami-collapsed nanofingers chip

Surface-Enhanced Raman Scattering (SERS) offers great potential for label-free molecular diagnosis, especially in detecting disease biomarkers. However, the complexity of the biological environment in clinical human serum often significantly impairs detection accuracy. In this study, we present a highly effective SERS strategy utilizing aptamer origami-collapsed nanofingers for the precise qualitative and quantitative detection of specific targeted biomarkers in clinical serum. Here, the biomarker-specific aptamers are anchored to gold nanofingers, which then collapse during liquid evaporation, forming sub-nanometric gaps that enhance near-field strength. The serum is introduced directly into these stabilized nanofingers, where targeted biomarkers are selectively captured in aptamer hotspots, yielding pure Raman spectra of the biomarkers without interference from other serum molecules. The ratio of the biomarker's characteristic Raman peak to that of the aptamer allows for accurate quantification. This approach was validated with alpha-fetoprotein (AFP) for hepatocellular carcinoma and cardiac troponin I (cTnI) for acute myocardial infarction in clinical serum, achieving detection within 3 min. This strategy represents a significant advancement in SERS-based medical diagnostics, offering exceptional sensitivity and specificity in complex biological samples.

Gold nanorod in silver tetrahedron: Cysteamine mediated synthesis of SERS probes with embedded internal markers for AFP detection

BACKGROUND

Plasmonic core-shell nanostructures with embedded internal markers used as Raman probes have attracted great attention in surface-enhanced Raman scattering (SERS) immunoassay for cancer biomarkers due to their excellent uniform enhancement. However, current core-shell nanostructures typically exhibit a spherical shape and are coated with a gold shell, resulting in constrained local field enhancement.

RESULTS

In this work, we prepared a core-shell AuNR@BDT@Ag structure by depositing silver on the surface of Raman reporter-modified gold nanorods (AuNR). With cysteamine-driven specific deposition of Ag atoms, the internal standard nanoprobes with an ortho-tetrahedral morphology were obtained. Owing to its tetrahedral morphology and the effective plasmon coupling at the Ag-Au interface, this internal standard Raman probe exhibited excellent Raman enhancement. Also, with embedded Raman reporter, the probes of Au nanorod in Ag tetrahedron avoided the desorption of Raman reporter and competitive adsorption of interfering molecule, which greatly improved the stability and reproducibility of SERS signal and addressed the drawbacks of low reproducibility existing in SERS immunoassay. The feasibility of the AuNR@BDT@Ag probe was demonstrated by the sensitive detection of the liver cancer biomarker alpha-fetoprotein (AFP) in Eppendorf (EP) tubes and microfluidic chips. The results in EP tubes revealed a linear range of 1 fg/mL-1 ng/mL and a detection limit of 0.631 fg/mL. When the detection was performed in microfluidic chips, the linear range was 10 pg/mL to 0.1 μg/mL, with a limit detection of 8.29 pg/mL.

SIGNIFICANCE

The performance of AFP detection in EP tubes and microfluidic chips demonstrates that the tetrahedral core-shell AuNR@BDT@Ag nanostructures used as internal standard Raman probes have the potential to detect biomarkers in blood samples for cancer screening.

Enhanced photocurrents for photoelectrochemical immunoassay of alpha-fetoprotein with Pt-functionalized Bi2O2S nanoflowers

BACKGROUND

Designing heterojunctions with efficient electron-hole separation holds great promise for improving photoelectric response.

RESULTS

Herein, we reported a multifunctional Pt co-catalyst-modified Bi2O2S nanoflowers (BOS NFs) photocatalytic component for achieving an efficient photoelectric chemistry (PEC) immunosensor for alpha-fetoprotein (AFP). Briefly, the Pt co-catalyst improved the intrinsic band gap structure of BOS on the one hand, and on the other hand, it was able to achieve a rapid decomposition of hydrogen peroxide to hydroxyl radicals, which led to the improvement of electrochemical half-responses during the amplification of target immunosignals. In addition, Pt-functionalized BOS NFs (BOS-Pt) exhibited peroxidase-like enzymatic reaction activity and related properties. By enzyme-linked immunosorbent assay, a sandwich immuno-model in the presence of AFP catalyzed the production of hydrogen peroxide from the substrate glucose and the conversion of a sizable photoelectrochemical signal catalyzed by BOS-Pt. Following condition optimization, it was determined that the developed sensor exhibited a specific response to AFP over a wide linear range of 0.05-50 ng mL-1.

SIGNIFICANCE

This work provides a new strategy for developing efficient immunosensors from the perspective of modulating photoelectrochemical half-reactions.

Preparation of cellulose-based flexible SERS and its application for rapid and ultra-sensitive detection of thiram on fruits and vegetables

In response to the prevalent issue of thiram as a common pesticide residue on the surface of fruits and vegetables, our research team employed an acidic hydrated metal salt low co-fusion solvent to dissolve cellulose lysis slurry. Subsequently, a regenerated cellulose membrane (RCM) was successfully prepared via sol-gel method. Uniformly sized Ag nanoparticles (NPs) were deposited on RCM utilizing the continuous ion layer adsorption and reaction (SILAR) technique. The resulting Ag NPs/RCM flexible surface-enhanced Raman spectroscopy (SERS) substrates exhibited a minimum detection limit of 5 × 10-9 M for Rhodamine 6G (R6G), demonstrating good uniformity (RSD = 4.86 %) and reproducibility (RSD = 3.07 %). Moreover, the substrate displayed a remarkable sensitivity of 10-10 M toward thiram standard solution. Given its inherent flexibility, the substrate proves advantageous for the detection of three-dimensional environments such as fruit and vegetable surfaces, and its practicality has been confirmed in the detection of thiram residue on apples, tomatoes, pears, and other fruits and vegetables.

3D SERS Substrate of Z-Shaped Ag Nanorod Array for Thiabendazole Detection

Ag nanoparticles sputtered on silicon wafer are used as masks for the fabrication of silicon columns by ion etching, which induces the growth of the inclined Ag nanorod by inclined Ag sputtering. V-shaped and Z-shaped Ag nanorods can be obtained by varying incline angles and deposition times. SERS detection and FDTD simulation are used to compare and investigate the enhanced electromagnetic coupling of incline nanorod arrays with different shapes in three-dimensional space, which indicates that Z-shaped nanorods show good SERS properties. The Z-shaped Ag nanorod array is used as a SERS substrate for the detection of thiabendazole with a concentration down to 10-11 M.

Raman Scattering-Based Optical Sensing Of Chronic Liver Diseases

Chronic liver diseases (CLDs) are a major public health problem. Despite the progress achieved in fighting against viral hepatitis, the emergence of non-alcoholic fatty liver disease might pose a serious challenge to the public's health in the coming decades. Medical management of CLDs represents a substantial burden on the public health infrastructures. The health care cost of these diseases is an additional burden that weighs heavily on the economies of developing countries. Effective management of CLDs requires the adoption of reliable and cost-effective screening and diagnosing methods to ensure early detection and accurate clinical assessment of these diseases. Vibrational spectroscopies have emerged as universal analytical methods with promising applications in various industrial and biomedical fields. These revolutionary analytical techniques rely on analyzing the interaction between a light beam and the test sample to generate a spectral fingerprint. This latter is defined by the analyte's chemical structure and the molecular vibrations of its functional groups. Raman spectroscopy and surface-enhanced Raman spectroscopy have been used in combination with various chemometric tests to diagnose a wide range of malignant, metabolic and infectious diseases. The aim of the current review is to cast light on the use of these optical sensing methods in the diagnosis of CLDs. The vast majority of research works that investigated the potential application of these spectroscopic techniques in screening and detecting CLDs were discussed here. The advantages and limitations of these modern analytical methods, as compared with the routine and gold standard diagnostic approaches, were also reviewed in details.

Plasmonic Biosensors with Nanostructure for Healthcare Monitoring and Diseases Diagnosis

Nanophotonics has been widely utilized in enhanced molecularspectroscopy or mediated chemical reaction, which has major applications in the field of enhancing sensing and enables opportunities in developing healthcare monitoring. This review presents an updated overview of the recent exciting advances of plasmonic biosensors in the healthcare area. Manufacturing, enhancements and applications of plasmonic biosensors are discussed, with particular focus on nanolisted main preparation methods of various nanostructures, such as chemical synthesis, lithography, nanosphere lithography, nanoimprint lithography, etc., and describing their respective advances and challenges from practical applications of plasmon biosensors. Based on these sensing structures, different types of plasmonic biosensors are summarized regarding detecting cancer biomarkers, body fluid, temperature, gas and COVID-19. Last, the existing challenges and prospects of plasmonic biosensors combined with machine learning, mega data analysis and prediction are surveyed.

Flexible SERS Substrate with a Ag-SiO2 Cosputtered Film for the Rapid and Convenient Detection of Thiram

It is very important to build uniform large-area dense hotspots to improve the surface-enhanced Raman scattering (SERS) detection limit. In our research, we designed and prepared a new flexibile SERS substrate with ultradense hot spots that has the advantages of high sensitivity, good repeatability, easy fabrication, and low cost. Due to the special dense hot spot structure, the substrate reaches a SERS enhancement factor of 2.1 × 10¹¹. Because of the excellent physical stability of polydimethylsiloxane, the substrate can be bent at will, and the SERS performance will not change with bending. This is very important to extract effective detection objects on complex surfaces. The substrate has good light transmittance and softness and can be directly attached to the detected agricultural products to realize real-time and rapid SERS monitoring. This structure exhibits extraordinary performance for thiram detection in the ultralow concentration range of 10^-13 M.

Recent Progress on Solid Substrates for Surface-Enhanced Raman Spectroscopy Analysis

Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique with distinguished features of non-destructivity, ultra-sensitivity, rapidity, and fingerprint characteristics for analysis and sensors. The SERS signals are mainly dependent on the engineering of high-quality substrates. Recently, solid SERS substrates with diverse forms have been attracting increasing attention due to their promising features, including dense hot spot, high stability, controllable morphology, and convenient portability. Here, we comprehensively review the recent advances made in the field of solid SERS substrates, including their common fabrication methods, basic categories, main features, and representative applications, respectively. Firstly, the main categories of solid SERS substrates, mainly including membrane substrate, self-assembled substrate, chip substrate, magnetic solid substrate, and other solid substrate, are introduced in detail, as well as corresponding construction strategies and main features. Secondly, the typical applications of solid SERS substrates in bio-analysis, food safety analysis, environment analysis, and other analyses are briefly reviewed. Finally, the challenges and perspectives of solid SERS substrates, including analytical performance improvement and largescale production level enhancement, are proposed.

A Glycoform-Resolved Dual-Modal Ratiometric Immunoassay Improves the Diagnostic Precision for Hepatocellular Carcinoma

The glycosylation pattern of alpha fetoprotein (AFP) paves the basis for precise early diagnosis of hepatocellular carcinoma (HCC). However, existing analytical methods ignore the contribution of terminal sialic acid, which has been reported to be highly connected with HCC. Besides, the development of diagnostic assays is severely hindered by the preparation of anti-glycans antibodies. Molecularly imprinted polymers (MIPs), as synthetic antibody mimics, provide unique strengths to address these issues. Herein, we report a MIPs-based dual-modal ratiometric immunoassay for precise HCC diagnosis. Using a "pit one against ten" MIP to recognize a subset of glycans containing sialic acid and/or core fucose, we demonstrated our assay exhibited improved precision as compared with ELISA. This assay provided not only a glycoform-resolved method for precise HCC diagnosis, but also a new paradigm for developing antibody mimics via molecular imprinting towards challenging biomedical applications.

High-performance surface-enhanced Raman spectroscopy chip integrated with a micro-optical system for the rapid detection of creatinine in serum

To improve the sensitivity of disease biomarker detection, we proposed a high-performance surface-enhanced Raman spectroscopy (SERS) chip integrated with a micro-optical system (MOS). The MOS, which is based on the micro-reflecting cavity and the micro-lens, optimizes the optical matching characteristics of the SERS substrate and the Raman detection system, and greatly improves the SERS detection sensitivity by improving the collection efficiency of the Raman scattering signal. A uniform single layer of silver nanoparticles on a gold film was prepared as the SERS substrate using a liquid-liquid interface self-assembly method. The micro-reflecting cavity and micro-lens were prepared using micro-processing technology. The SERS chip was constructed based on the MOS and the Au film-based SERS substrate, and experimental results showed an EF of 1.46×10⁸, which is about 22.4 times higher than that of the Si-based SERS substrate. The chip was used for the detection of creatinine and the detection limit of creatinine in aqueous solution was 1 µM while the detection limit in serum was 5 µM. In addition, SERS testing was conducted on serum samples from normal people and patients with chronic renal impairment. Principal component analysis and linear discriminant analysis were used for modeling and identification, and the results showed a 90% accuracy of blind sample detection. These results demonstrate the value of this SERS chip for both research and practical applications in the fields of disease diagnosis and screening.

Polarized SERS Controlled by Anisotropic Growth on Ordered Curvature Substrate

Colloidal lithography is an efficient and low-cost method to prepare an ordered nanostructure array with new shapes and properties. In this study, square-shaped and cone-shaped Au nanostructures were obtained by 70° angle deposition onto polystyrene bead array with the diameter of 500 nm when a space of 120 nm is created between the neighbor beads by plasma etching. The gaps between the units decrease when the Au deposition time increases, which leads to the polarized enhanced local field, in agreement with the surface-enhanced Raman scattering spectra (SERS) observations and finite-difference time-domain (FDTD) simulations. When the Au deposition time increased to 5 min, 5 nm gaps form between the neighbor units, which gave an enhancement factor of 5 × 10⁹. The SERS chip was decorated for the detection of the liver cancer cell marker Alpha-fetoprotein (AFP) with the detection limit down to 5 pg/mL.

Plasmonic structure with nanocavity cavities for SERS detection of pesticide thiram

Excessive thiram residues in food have the potential to negatively impact human health. Hence, the development of a convenient and fast detection method is highly desirable. In this study, an efficient, repeatable, and sensitive surface-enhanced Raman scattering (SERS) active chip was manufactured via a low-cost colloidal lithography technique. The plasmonic structure was composed of a series of silver nanospheres and nanowires. Interestingly, this type structure creates a nanocavity space with a characteristic geometry generating a strong electromagnetic field coupling. The finite-different time-domain software was employed to simulate the electromagnetic field distribute on the nanocavity. Accordingly, SERS active chip that displays ultra-low concentration detection of thiram (10^-11 M) was realized. Moreover, the excellent reproducibility of thiram (10^-6 M) practical detection on an apple pericarp has great potential for application in food safety.

Self-sustainable and recyclable ternary Au@Cu2O-Ag nanocomposites: application in ultrasensitive SERS detection and highly efficient photocatalysis of organic dyes under visible light

Ternary noble metal-semiconductor nanocomposites (NCs) with core-shell-satellite nanostructures have received widespread attention due to their outstanding performance in detecting pollutants through surface-enhanced Raman scattering (SERS) and photodegradation of organic pollutants. In this work, ternary Au@Cu2O-Ag NCs were designed and prepared by a galvanic replacement method. The effect of different amounts of Ag nanocrystals adsorbed on the surfaces of Au@Cu2O on the SERS activity was investigated based on the SERS detection of 4-mercaptobenzoic acid (4-MBA) reporter molecules. Based on electromagnetic field simulations and photoluminescence (PL) results, a possible SERS enhancement mechanism was proposed and discussed. Moreover, Au@Cu2O-Ag NCs served as SERS substrates, and highly sensitive SERS detection of malachite green (MG) with a detection limit as low as 10-9 M was achieved. In addition, Au@Cu2O-Ag NCs were recycled due to their superior self-cleaning ability and could catalyze the degradation of MG driven by visible light. This work demonstrates a wide range of possibilities for the integration of recyclable SERS detection and photodegradation of organic dyes and promotes the development of green testing techniques.

High signal collection efficiency in a 3D SERS chip using a micro-reflector

To improve the sensitivity of surface-enhanced Raman spectroscopy (SERS) detection, we propose a three-dimensional (3D) SERS chip based on an inverted pyramid micro-reflector (IPMR) that converges Raman scattering light signals to improve the signal collection efficiency. The influence of the geometric parameters of the inverted pyramid structure on the Raman signal collection efficiency was analyzed by simulation for the determination of the optimal design parameters. The inverted pyramid through-hole structure was prepared on the silicon wafer through an anisotropic wet etching process, followed by the sputtering of a gold film to form the IPMR. The 3D SERS chip was constructed by bonding the IPMR and the active substrate that assembled with silver nanoparticles. Using Rhodamine 6G molecules, the Raman intensity measured with the 3D SERS chip was threefold greater than that of the silicon-based SERS substrate under the same test conditions. These experimental results show that the 3D SERS chip can significantly improve the SERS signal intensity. Its 3D structure is convenient for integration with microfluidic devices and has great potential in biochemical detection applications.

Manipulation and Applications of Hotspots in Nanostructured Surfaces and Thin Films

The synthesis of nanostructured surfaces and thin films has potential applications in the field of plasmonics, including plasmon sensors, plasmon-enhanced molecular spectroscopy (PEMS), plasmon-mediated chemical reactions (PMCRs), and so on. In this article, we review various nanostructured surfaces and thin films obtained by the combination of nanosphere lithography (NSL) and physical vapor deposition. Plasmonic nanostructured surfaces and thin films can be fabricated by controlling the deposition process, etching time, transfer, fabrication routes, and their combination steps, which manipulate the formation, distribution, and evolution of hotspots. Based on these hotspots, PEMS and PMCRs can be achieved. This is especially significant for the early diagnosis of hepatocellular carcinoma (HCC) based on surface-enhanced Raman scattering (SERS) and controlling the growth locations of Ag nanoparticles (AgNPs) in nanostructured surfaces and thin films, which is expected to enhance the optical and sensing performance.