A nanoplasmonic biosensor for label-free multiplex detection of cancer biomarkers

Distinguishable Magnetic Reporter Coordination with Buoyancy-Magnetism Separation for Immobilization-Free Dual-Target Electrochemical Immunosensing

Simultaneous sensitive and precise determination of multibiomarkers is of great significance for improving detection efficiency, reducing diagnosis and treatment expenses, and elevating survival rates. However, the development of simple and portable biosensors for simultaneous determination of multiplexed targets in biological fluids still faces challenges. Herein, a unique and versatile immobilization-free dual-target electrochemical biosensing platform, which combines distinguishable magnetic signal reporters with buoyancy-magnetism separation, was designed and constructed for simultaneous detection of carcinoembryonic (CEA) and α-fetoprotein (AFP) in intricate biological fluids. To construct such distinguishable magnetic signal reporters with signal transduction, amplification, and output, secondary antibodies of CEA and AFP were respectively functionalized on methylene blue (MB) and 6-(ferrocenyl)hexanethiol (FeC) modified Fe3O4@Au magnetic nanocomposites. Meanwhile, a multifunctional flotation probe with dual target recognition, capture, and isolation capability was prepared by conjugating primary antibodies (Ab1-CEA, Ab1-AFP) to hollow buoyant microspheres. The target antigens of CEA and AFP can trigger a flotation-mediated sandwich-type immunoreaction and capture a certain amount of the distinguishable magnetic signal reporter, which enables the conversion of the target CEA and AFP quantities to the signal of the potential-resolved MB and FeC. Thus, the MB and FeC currents of magnetically adsorbed distinguishable magnetic reporters can be used to determine the CEA and AFP targets simultaneously and precisely. Accordingly, the proposed strategy exhibited a delightful linear response for CEA and AFP in the range of 100 fg·mL-1-100 ng·mL-1 with detection limits of 33.34 and 17.02 fg·mL-1 (S/N = 3), respectively. Meanwhile, no significant nonspecific adsorption and cross-talk were observed. The biosensing platform has shown satisfactory performance in the determination of real clinical samples. More importantly, the proposed approach can be conveniently extended to universal detection just by simply substituting biorecognition events. Thus, this work opens up a new promising perspective for dual and even multiple targets and offers promising potential applications in clinical diagnosis.

Optical nanomaterial-based detection of biomarkers in liquid biopsy

Liquid biopsy, which is a minimally invasive procedure as an alternative to tissue biopsy, has been introduced as a new diagnostic/prognostic measure. By screening disease-related markers from the blood or other biofluids, it promises early diagnosis, timely prognostication, and effective treatment of the diseases. However, there will be a long way until its realization due to its conceptual and practical challenges. The biomarkers detected by liquid biopsy, such as circulating tumor cell (CTC) and circulating tumor DNA (ctDNA), are extraordinarily rare and often obscured by an abundance of normal cellular components, necessitating ultra-sensitive and accurate detection methods for the advancement of liquid biopsy techniques. Optical biosensors based on nanomaterials open an important opportunity in liquid biopsy because of their enhanced sensing performance with simple and practical properties. In this review article, we summarized recent innovations in optical nanomaterials to demonstrate the sensitive detection of protein, peptide, ctDNA, miRNA, exosome, and CTCs. Each study prepares the optical nanomaterials with a tailored design to enhance the sensing performance and to meet the requirements of each biomarker. The unique optical characteristics of metallic nanoparticles (NPs), quantum dots, upconversion NPs, silica NPs, polymeric NPs, and carbon nanomaterials are exploited for sensitive detection mechanisms. These recent advances in liquid biopsy using optical nanomaterials give us an opportunity to overcome challenging issues and provide a resource for understanding the unknown characteristics of the biomarkers as well as the mechanism of the disease.

Novel SERS Signal Amplification Strategy for Ultrasensitive and Specific Detection of Spinal Cord Injury-Related miRNA

The expression of microRNA (miRNA) changes in many diseases plays an important role in the diagnosis, treatment, and prognosis of diseases. Spinal cord injury (SCI) is a serious disease of the central nervous system, accompanied by inflammation, cell apoptosis, neuronal necrosis, axonal rupture, demyelination, and other pathological processes, resulting in impaired sensory and motor functions of patients. Studies have shown that miRNA expression has changed after SCI, and miRNAs participate in the pathophysiological process and treatment of SCI. Therefore, quantitative analysis and monitoring of the expression of miRNA were of great significance for the diagnosis and treatment of SCI. Through the SCI-related miRNA chord plot, we screened out miRNA-21-5p and miRNA-let-7a with a higher correlation. However, for traditional detection strategies, it is still a great challenge to achieve a fast, accurate, and sensitive detection of miRNA in complex biological environments. The most frequently used method for detecting miRNAs is polymerase chain reaction (PCR), but it has disadvantages such as being time-consuming and cumbersome. In this paper, a novel SERS sensor for the quantitative detection of miRNA-21-5p and miRNA-let-7a in serum and cerebrospinal fluid (CSF) was developed. The SERS probe eventually formed a sandwich-like structure of Fe3O4@hpDNA@miRNA@hpDNA@GNCs with target miRNAs, which had high specificity and stability. This SERS sensor achieved a wide range of detection from 1 fM to 1 nM and had a good linear relationship. The limits of detection (LOD) for miRNA-21-5p and miRNA-let-7a were 0.015 and 0.011 fM, respectively. This new strategy realized quantitative detection and long-term monitoring of miRNA-21-5p and miRNA-let-7a in vivo. It is expected to become a powerful biomolecule analysis tool and will provide ideas for the diagnosis and treatment of many diseases.

Surface plasmonic biosensors: principles, designs and applications

Recently, surface plasmon resonance (SPR) biosensors have been widely used in environmental monitoring, food contamination detection and diagnosing medical conditions due to their superior sensitivity, label-free detection and rapid analysis speed. This paper briefly elaborates on the development history of SPR technology and introduces SPR signal sensing principles. A summary of recent applications of SPR sensors in different fields is highlighted, including their figures of merit and limitations. Finally, the personal perspectives and future development trends about sensor preparation and design are discussed in detail, which may be critical for improving the performance of SPR sensors.

Plasmonic metasurface enhanced by nanobumps for label-free biosensing of lung tumor markers in serum

Plasmonic metasurface biosensing has excellent potential in label-free detection of tumor biomarkers. In general, a variety of plasmonic metasurface nanofabrication leads to various degree of metallic surface roughness. However, the metasurface roughness effects on plasmonic sensing of tumor markers have been barely reported. Here we fabricate high-roughness (HR) gold nanohole metasurfaces with nanobumps and investigate their biosensing in comparison with the low-roughness (LR) counterparts. The HR metasurfaces demonstrate the surface sensitivity of multilayer polyelectrolyte molecules, which is 57.0% higher than the LR ones. The HR metasurfaces also illuminate higher immunoassay sensitivity to multiple lung cancer biomarkers, including carcinoembryonic antigen, neuron-specific enolase and cytokeratin fragment 21-1. The highest increasement of tumor marker sensitivity is up to 71.4%. The biosensing enhancement is attributed to the introduction of gold nanobumps on metasurfaces, which provides more hot-spot regions, higher localized near-field intensity and better optical impedance matching. Furthermore, the biosensing of HR metasurfaces effectively covers the threshold values of tumor markers for early lung cancer diagnosis, and is used for the detection of clinical serum samples. The testing deviation is less than 4% compared with commercial immunoassay, which implies promising applications on medical examinations. Our research provides a scientific guide to surface roughness engineering for plasmonic metasensing in the future point-of-care testing.

Surface Plasmon Resonance (SPR) Sensor for Cancer Biomarker Detection

A biomarker is a physiological observable marker that acts as a stand-in and, in the best-case scenario, forecasts a clinically significant outcome. Diagnostic biomarkers are more convenient and cost-effective than directly measuring the ultimate clinical outcome. Cancer is among the most prominent global health problems and a major cause of morbidity and death globally. Therefore, cancer biomarker assays that are trustworthy, consistent, precise, and verified are desperately needed. Biomarker-based tumor detection holds a lot of promise for improving disease knowledge at the molecular scale and early detection and surveillance. In contrast to conventional approaches, surface plasmon resonance (SPR) allows for the quick and less invasive screening of a variety of circulating indicators, such as circulating tumor DNA (ctDNA), microRNA (miRNA), circulating tumor cells (CTCs), lipids, and proteins. With several advantages, the SPR technique is a particularly beneficial choice for the point-of-care identification of biomarkers. As a result, it enables the timely detection of tumor markers, which could be used to track cancer development and suppress the relapse of malignant tumors. This review emphasizes advancements in SPR biosensing technologies for cancer detection.

Rapid magnetic separation: An immunoassay platform for the SERS-based detection of subarachnoid hemorrhage biomarkers

The blood–brain barrier (BBB) is of vital importance to the progression and prognosis of subarachnoid hemorrhage (SAH). The construction of a simple, sensitive, and accurate detection assay for measuring the biomarkers associated with BBB injury is still an urgent need owing to the complex pathogenesis of SAH and low expression levels of pathological molecules. Herein, we introduced surface-enhanced Raman scattering (SERS) label-embedded Fe₃O₄@Au core-shell nanoparticles as ideal SERS sensors for quantitative double detection of MMP-9 and occludin in SAH patients. Meanwhile, utilizing the SERS signals to dynamically estimate MMP-9 and occludin concentration in the rat SAH model is the first application in exploring the relationship of pathological MMP-9 and occludin molecular levels with neurobehavioral score. This method warrants reliable detection toward MMP-9 and occludin with a wide recognition range and a low detection limit in blood samples. Furthermore, the results monitored by the SERS assay exactly matched with those obtained through a traditional enzyme-linked immunosorbent assay (ELISA). The aforementioned results demonstrated this novel biosensor strategy has extensive application prospects in the quantitative measurement of multiple types of biomolecules in body fluid samples.

A Sensitive and Portable Double-Layer Microfluidic Biochip for Harmful Algae Detection

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, rapid and portable double-layer microfluidic biochip for the simultaneous quantitative detection of six species of algae. Specific DNA probes based on the 18S ribosomal DNA (18S rDNA) gene fragments of HABs were designed and labeled with the fluorescent molecule cyanine-3 (Cy3). The biochip had multiple graphene oxide (GO) nanosheets-based reaction units, in which GO nanosheets were applied to transfer target DNA to the fluorescence signal through a photoluminescence detection system. The entire detection process of multiple algae was completed within 45 min with the linear range of fluorescence recovery of 0.1 fM-100 nM, and the detection limit reached 108 aM. The proposed approach has a simple detection process and high detection performance and is feasible to conduct accurate detection with matched portable detection equipment. It will have promising applications in marine natural disaster monitoring and environmental care.

Quantitative and Noninvasive Detection of SAH-Related MiRNA in Cerebrospinal Fluids In Vivo Using SERS Sensors Based on Acupuncture-Based Technology

Quantitative analysis of microRNAs (miRNAs) in a noninvasive manner is of vital importance for disease diagnosis and prognosis evaluation. However, conventional strategies for realizing accurate, simple, and sensitive detection of target molecules are still a challenge, especially for miRNAs due to their low abundance and susceptibility in the complex biological environment. Here, a novel surface-enhanced Raman scattering (SERS) strategy was established for quantitative detection and monitoring of miRNA-21-5p (miR-21-5p) in living cells and in vivo cerebrospinal fluid (CSF) by applying hairpin DNA (hpDNA)-conjugated gold nanostars (GNSs) SERS probes combined with acupuncture-based technology. This strategy enabled ultrasensitive exploration toward miR-21-5p in a wide range from 1 fM to 100 pM in cell lysates. Moreover, SERS analysis facilitated the detection and long-term monitoring for in vivo miR-21-5p noninvasively. This developed strategy promises to offer a powerful method for the analysis of multiple biomolecules in single cells and living bodies.

Multiplexed Homogeneous Immunoassay Based on Counting Single Immunocomplexes together with Dark-Field and Fluorescence Microscopy

The development of multiplexed immunoassays is impeded by the difficulty in distinguishing labeled immunocomplexes from free probes and nonspecifically bound probes. Here, we attempted to overcome this issue by counting core-satellite-structured immunocomplexes simultaneously using dark-field and fluorescence microscopy. The tumor biomarkers of carcinoembryonic antigen (CEA), α-fetoprotein (AFP), and prostate-specific antigen (PSA) were chosen as model targets. Gold nanoparticles (AuNPs) with diameters of 70 nm were coated with the detection antibodies of the three targets. Quantum dot (QD) 525, QD 585, and QD 655 were modified with the capture antibodies of CEA, AFP, and PSA, respectively. Then, an immunocomplex containing one AuNP and one or several QDs was formed, whereas free and nonspecifically bound probes had either one AuNP or one QD. When observed with a transmission grating-based spectral microscope, the immunocomplexes had overlapping scattering and fluorescent spectral images and were therefore identified and quantified precisely. The biomarkers inside the immunocomplexes were recognized on the basis of the fluorescent first-order streaks of the QDs. Model biomarkers in buffer and in 12.6% blank plasma were quantified for validation. The limits of detection for CEA, PSA, and AFP in buffer were in dozens of femtomolar and were close to those in blank plasma. The results demonstrated that our approach worked well in distinguishing immunocomplexes from free and nonspecifically bound probes. The successful quantification of the three targets in five human plasma samples verified the reliability of our method in clinical applications.

Nanoplasmonic multiplex biosensing for COVID-19 vaccines

The ongoing emergence of severe acute respiratory syndrome caused by the new coronavirus (SARS-CoV-2) variants requires swift actions in identifying specific antigens and optimizing vaccine development to maximize the humoral response of the patient. Measuring the specificity and the amount of antibody produced by the host immune system with high throughput and accuracy is critical to develop timely diagnostics and therapeutic strategies. Motivated by finding an easy-to-use and cost-effective alternative to existing serological methodologies for multiplex analysis, we develop a proof-of-concept multiplex nanoplasmonic biosensor to capture the humoral response in serums against multiple antigens. Nanoplasmonic sensing relies on the wavelength shift of the localized surface plasmon resonance (LSPR) peak of gold nanostructures upon binding interactions between the antibodies and the immobilized antigens. Here the antigens are first immobilized on different sensing areas by using a mono-biotinylation system based on the high affinity interaction between biotin and streptavidin. We then validate the multiplex platform by detecting the presence of 3 monoclonal antibodies against 3 antigens (2 different hemagglutinins (HAs) from influenza viruses, and the SARS-CoV-2 Spike RBD (receptor binding domain)). We also measure the humoral response in murine sera collected before and after its immunization with the SARS-CoV-2 Spike protein, in good agreement with the results obtained by the ELISA assay. Our nanoplasmonic assays have successfully demonstrated multiple serum antibody profiling, which can be further integrated with microfluidics as an effective high throughput screening platform in future studies for the ongoing SARS-CoV-2 vaccine development.

Rapid and High‐Throughput SARS‐CoV‐2 RNA Detection without RNA Extraction and Amplification by Using a Microfluidic Biochip

The ongoing outbreak of the severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2) has spread globally and poses a threat to public health and National economic development. Rapid and high‐throughput SARS‐CoV‐2 RNA detection without the need of RNA extraction and amplification remain a key challenge. In this study, a new SARS‐CoV‐2 RNA detection strategy using a microfluidic biochip for the rapid and ultrasensitive detection of SARS‐CoV‐2 without RNA extraction and amplification was developed. This new strategy takes advantage of the specific SARS‐CoV‐2 RNA and probe DNA reaction in the microfluidic channel, fluorescence signal regulation by nanomaterials, and accurate sample control by the microfluidic chip. It presents an ultralow limit of detection of 600 copies mL⁻¹ in a large linear detection regime from 1 aM to 100 fM. Fifteen samples were simultaneously detected in 40 min without the need for RNA purification and amplification. The detection accuracy of the strategy was validated through quantitative reverse transcription polymerase chain reaction (qRT‐PCR), with a recovery of 99–113 %. Therefore, the SARS‐CoV‐2 RNA detection strategy proposed in this study can potentially be used for the quantitative diagnosis of viral infectious diseases.

Advances in surface plasmon resonance-based biosensor technologies for cancer biomarker detection

Surface plasmon resonance approach is a highly useful option to offer optical and label-free detection of target bioanalytes with numerous advantages (e.g., low-cost fabrication, appreciable sensitivity, label-free detection, and outstanding accuracy). As such, it allows early diagnosis of cancer biomarkers to monitor tumor progression and to prevent the recurrence of oncogenic tumors. This work highlights the recent progress in SPR biosensing technology for the diagnosis of various cancer types (e.g., lung, breast, prostate, and ovarian). Further, the performance of various SPR biosensors is also evaluated in terms of the basic quality assurance criteria (e.g., limit of detection (LOD), selectivity, sensor response time, and reusability). Finally, the limitations and future challenges associated with SPR biosensors are also discussed with respect to cancer biomarker detection.

Mechanical Stress Induces a Transient Suppression of Cytokine Secretion in Astrocytes Assessed at the Single-Cell Level with a High-Throughput Microfluidic Chip

Brain cells are constantly subjected to mechanical signals. Astrocytes are the most abundant glial cells of the central nervous system (CNS), which display immunoreactivity and have been suggested as an emerging disease focus in the recent years. However, how mechanical signals regulate astrocyte immunoreactivity, and the cytokine release in particular, remains to be fully characterized. Here, human neural stem cells are used to induce astrocytes, from which the release of 15 types of cytokines are screened, and nine of them are detected using a protein microfluidic chip. When a gentle compressive force is applied, altered cell morphology and reinforced cytoskeleton are observed. The force induces a transient suppression of cytokine secretions including IL-6, MCP-1, and IL-8 in the early astrocytes. Further, using a multiplexed single-cell culture and protein detection microfluidic chip, the mechanical effects at a single-cell level are analyzed, which validates a concerted downregulation by force on IL-6 and MCP-1 secretions in the cells releasing both factors. This work demonstrates an original attempt of employing the protein detection microfluidic chips in the assessment of mechanical regulation on the brain cells at a single-cell resolution, offering novel approach and unique insights for the understanding of the CNS immune regulation.

The Challenges of Developing Biosensors for Clinical Assessment: A Review

Emerging research in biosensors has attracted much attention worldwide, particularly in response to the recent pandemic outbreak of coronavirus disease 2019 (COVID-19). Nevertheless, initiating research in biosensing applied to the diagnosis of diseases is still challenging for researchers, be it in the preferences of biosensor platforms, selection of biomarkers, detection strategies, or other aspects (e.g., cutoff values) to fulfill the clinical purpose. There are two sides to the development of a diagnostic tool: the biosensor development side and the clinical side. From the development side, the research engineers seek the typical characteristics of a biosensor: sensitivity, selectivity, linearity, stability, and reproducibility. On the other side are the physicians that expect a diagnostic tool that provides fast acquisition of patient information to obtain an early diagnosis or an efficient patient stratification, which consequently allows for making assertive and efficient clinical decisions. The development of diagnostic devices always involves assay developer researchers working as pivots to bridge both sides whose role is to find detection strategies suitable to the clinical needs by understanding (1) the intended use of the technology and its basic principle and (2) the preferable type of test: qualitative or quantitative, sample matrix challenges, biomarker(s) threshold (cutoff value), and if the system requires a mono- or multiplex assay format. This review highlights the challenges for the development of biosensors for clinical assessment and its broad application in multidisciplinary fields. This review paper highlights the following biosensor technologies: magnetoresistive (MR)-based, transistor-based, quartz crystal microbalance (QCM), and optical-based biosensors. Its working mechanisms are discussed with their pros and cons. The article also gives an overview of the most critical parameters that are optimized by developing a diagnostic tool.

Fast, accurate, point-of-care COVID-19 pandemic diagnosis enabled through advanced lab-on-chip optical biosensors: Opportunities and challenges

The sudden rise of the worldwide severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic in early 2020 has called into drastic action measures to perform instant detection and reduce the rate of spread. Common clinical and nonclinical diagnostic testing methods have been partially effective in satisfying the increasing demand for fast detection point-of-care (POC) methods to slow down further spread. However, accurate point-of-risk diagnosis of this emerging viral infection is paramount as the need for simultaneous standard operating procedures and symptom management of SARS-CoV-2 will be the norm for years to come. A sensitive, cost-effective biosensor with mass production capability is crucial until a universal vaccination becomes available. Optical biosensors can provide a noninvasive, extremely sensitive rapid detection platform with sensitivity down to ∼67 fg/ml (1 fM) concentration in a few minutes. These biosensors can be manufactured on a mass scale (millions) to detect the COVID-19 viral load in nasal, saliva, urine, and serological samples, even if the infected person is asymptotic. Methods investigated here are the most advanced available platforms for biosensing optical devices that have resulted from the integration of state-of-the-art designs and materials. These approaches include, but are not limited to, integrated optical devices, plasmonic resonance, and emerging nanomaterial biosensors. The lab-on-chip platforms examined here are suitable not only for SARS-CoV-2 spike protein detection but also for other contagious virions such as influenza and Middle East respiratory syndrome (MERS).

Functional Micro-/Nanomaterials for Multiplexed Biodetection

When analyzing biological phenomena and processes, multiplexed biodetection has many advantages over single-factor biodetection and is highly relevant to both human health issues and advancements in the life sciences. However, many key problems with current multiplexed biodetection strategies remain unresolved. Herein, the main issues are analyzed and summarized: 1) generating sufficient signal to label targets, 2) improving the signal-to-noise ratio to ensure total detection sensitivity, and 3) simplifying the detection process to reduce the time and labor costs of multiple target detection. Then, available solutions made possible by designing and controlling the properties of micro- and nanomaterials are introduced. The aim is to emphasize the role that micro-/nanomaterials can play in the improvement of multiplexed biodetection strategies. Through analyzing existing problems, introducing state-of-the-art developments regarding relevant materials, and discussing future directions of the field, it is hopeful to help promote necessary developments in multiplexed biodetection and associated scientific research.

Attomolar-Level Ultrasensitive and Multiplex microRNA Detection Enabled by a Nanomaterial Locally Assembled Microfluidic Biochip for Cancer Diagnosis

Non-invasive early diagnosis is of great significance in disease pathologic development and subsequent medical treatments, and microRNA (miRNA) detection has attracted critical attention in early cancer screening and diagnosis. High-throughput, sensitive, economic, and fast miRNA sensing platforms are necessary to realize the low-concentration miRNA detection in clinical diagnosis and biological studies. Here, we developed an attomolar-level ultrasensitive, rapid, and multiple-miRNA simultaneous detection platform enabled by nanomaterial locally assembled microfluidic biochips. This platform presents a large linear detection regime of 1 aM-10 nM, an ultralow detection limit of 0.146 aM with no amplification, a short detection time of 35 min with multiplex miRNA sensing capability, and a small sample volume consumption of 2 μL. The detection results of five miRNAs in real samples from breast cancer patients and healthy humans indicate its excellent capacity for practical applications in early cancer diagnosis. The proposed ultrasensitive, rapid, and multiple-miRNA detection microfluidic biochip platform is a universal miRNA detection approach and an important and valuable tool in early cancer screening and diagnosis as well as biological studies.

Ultrasensitive Point-of-Care Test for Tumor Marker in Human Saliva Based on Luminescence-Amplification Strategy of Lanthanide Nanoprobes

The point-of-care detection of tumor markers in saliva with high sensitivity and specificity remains a daunting challenge in biomedical research and clinical applications. Herein, a facile and ultrasensitive detection of tumor marker in saliva based on luminescence-amplification strategy of lanthanide nanoprobes is proposed. Eu2O3 nanocrystals are employed as bioprobes, which can be easily dissolved in acidic enhancer solution and transform into a large number of highly luminescent Eu3+ micelles. Meanwhile, disposable syringe filter equipped with nitrocellulose membrane is used as bioassay platform, which facilitates the accomplishment of detection process within 10 min. The rational integration of dissolution enhanced luminescent bioassay strategy and miniaturized detection device enables the unique lab-in-syringe assay of tumor marker like carcinoembryonic antigen (CEA, an important tumor marker in clinic diagnosis and prognosis of cancer) with a detection limit down to 1.47 pg mL-1 (7.35 × 10-15 m). Upon illumination with a portable UV flashlight, the photoluminescence intensity change above 0.1 ng mL-1 (0.5 × 10-12 m) of CEA can be visually detected by naked eyes, which allows one to qualitatively evaluate the CEA level. Moreover, we confirm the reliability of using the amplified luminescence of Eu2O3 nanoprobes for direct quantitation of CEA in patient saliva samples, thus validates the practicality of the proposed strategy for both clinical diagnosis and home self-monitoring of tumor marker in human saliva.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

Surface plasmon resonance biosensors for detection of Alzheimer's biomarkers; an effective step in early and accurate diagnosis

The rapid and direct detection of biomarkers in biofluids at clinically relevant concentrations faces serious limitations to develop diagnostic criteria for neurodegenerative diseases such as Alzheimer's disease (AD). In this regard, the early detection of biomarkers correlated with AD using novel modalities and instruments is at the center of attention. Recently, some newly invented optical-based biosensors namely Surface Plasmon Resonance (SPR) has been extensively investigated for the detection of biomarkers using a label-free method or by checking interaction between ligand and analyte. These approaches can sense a very small amount of target molecules in the blood and cerebrospinal fluids samples. In this review, the different hypothesis related to AD, and the structural properties of AD biomarkers was introduced. Also, we aim to highlight the specific role of available SPR-based sensing methods for early detection of AD biomarkers such as aggregated β-amyloid and tau proteins. Efforts to better understand the accuracy and efficiency of optical-based biosensors in the field of neurodegenerative disease enable us to accelerate the advent of novel modalities in the clinical setting for therapeutic and diagnostic purposes.

Dark-field hyperspectral imaging for label free detection of nano-bio-materials

Nanomaterials are playing an increasingly important role in cancer diagnosis and treatment. Nanoparticle (NP)-based technologies have been utilized for targeted drug delivery during chemotherapies, photodynamic therapy, and immunotherapy. Another active area of research is the toxicity studies of these nanomaterials to understand the cellular uptake and transport of these materials in cells, tissues, and environment. Traditional techniques such as transmission electron microscopy, and mass spectrometry to analyze NP-based cellular transport or toxicity effect are expensive, require extensive sample preparation, and are low-throughput. Dark-field hyperspectral imaging (DF-HSI), an integration of spectroscopy and microscopy/imaging, provides the ability to investigate cellular transport of these NPs and to quantify the distribution of them within bio-materials. DF-HSI also offers versatility in non-invasively monitoring microorganisms, single cell, and proteins. DF-HSI is a low-cost, label-free technique that is minimally invasive and is a viable choice for obtaining high-throughput quantitative molecular analyses. Multimodal imaging modalities such as Fourier transform infrared and Raman spectroscopy are also being integrated with HSI systems to enable chemical imaging of the samples. HSI technology is being applied in surgeries to obtain molecular information about the tissues in real-time. This article provides brief overview of fundamental principles of DF-HSI and its application for nanomaterials, protein-detection, single-cell analysis, microbiology, surgical procedures along with technical challenges and future integrative approach with other imaging and measurement modalities. This article is categorized under: Diagnostic Tools > in vitro Nanoparticle-Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging Implantable Materials and Surgical Technologies > Nanoscale Tools and Techniques in Surgery.

Progress in Neoantigen Targeted Cancer Immunotherapies

Immunotherapies that harness the immune system to kill cancer cells have showed significant therapeutic efficacy in many human malignancies. A growing number of studies have highlighted the relevance of neoantigens in recognizing cancer cells by intrinsic T cells. Cancer neoantigens are a direct consequence of somatic mutations presenting on the surface of individual cancer cells. Neoantigens are fully cancer-specific and exempt from central tolerance. In addition, neoantigens are important targets for checkpoint blockade therapy. Recently, technological innovations have made neoantigen discovery possible in a variety of malignancies, thus providing an impetus to develop novel immunotherapies that selectively enhance T cell reactivity for the destruction of cancer cells while leaving normal tissues unharmed. In this review, we aim to introduce the methods of the identification of neoantigens, the mutational patterns of human cancers, related clinical trials, neoantigen burden and sensitivity to immune checkpoint blockade. Moreover, we focus on relevant challenges of targeting neoantigens for cancer treatment.

Dielectric function modelling and sensitivity forecast for Au-Ag alloy nanostructures

Plasmonic metal nanostructures are promising for chemical and biological sensor applications due to their high spectral sensitivity, defined as the relative shift in resonance wavelength with respect to the refractive index changes of the surroundings. In this work, the refractive index sensitivity (RI sensitivity) of one kind of core-shell nanostructure was studied, in which the gold nanobipyramid (AuBP) core was sheltered by the Au-Ag alloy shell. We investigated the dependence of the RI sensitivity and the figure of merit (FOM) of the localized surface plasmon resonance (LSPR) on the geometry and the composition of the nanostructures. Theoretical consideration on the LSPR revealed that the RI sensitivity of the nanostructures is determined by the bulk plasma wavelength, dielectric properties of the alloy and the geometrical parameters. To quantitatively explore the dependence of the RI sensitivity on the metal compositions and the aspect ratios of the nanostructures, the frequency-related dielectric properties of the alloy were calculated using the Drude-critical points model (DCPM). Then the calculated dielectric data were applied in the finite difference time domain (FDTD) solutions to simulate the optical spectra of the alloy nanostructures with various Ag concentrations. Experimentally, a series of fabrication processes were also carried out for the growth of a homogeneous Au-Ag alloy nanoshell on the surface of AuBPs using a wet-chemical method. The measured RI sensitivities agree well with the values predicted from FDTD simulations, indicating the availability, credibility and feasibility of the modelled dielectric data of the alloy. The DCPM and FDTD simulations can be combined to calculate the dielectric properties and forecast the sensitivity properties of the Au-Ag alloyed nanostructures with varying concentrations.

Noble Metal-Assisted Surface Plasmon Resonance Immunosensors

For the early diagnosis of several diseases, various biomarkers have been discovered and utilized through the measurement of concentrations in body fluids such as blood, urine, and saliva. The most representative analytical method for biomarker detection is an immunosensor, which exploits the specific antigen-antibody immunoreaction. Among diverse analytical methods, surface plasmon resonance (SPR)-based immunosensors are emerging as a potential detection platform due to high sensitivity, selectivity, and intuitive features. Particularly, SPR-based immunosensors could detect biomarkers without labeling of a specific detection probe, as typical immunosensors such as enzyme-linked immunosorbent assay (ELISA) use enzymes like horseradish peroxidase (HRP). In this review, SPR-based immunosensors utilizing noble metals such as Au and Ag as SPR-inducing factors for the measurement of different types of protein biomarkers, including viruses, microbes, and extracellular vesicles (EV), are briefly introduced.

Rapid, quantitative and ultra-sensitive detection of cancer biomarker by a SERRS-based lateral flow immunoassay using bovine serum albumin coated Au nanorods

A rapid, sensitive, and stable SERRS-LFIA strip was developed for AFP detection using BSA-coated AuNRs as SERRS nanotags.

Are plasmonic optical biosensors ready for use in point-of-need applications?

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.

Gold nanoparticle amplification strategies for multiplex SPRi-based immunosensing of human pancreatic islet hormones

In this work, we demonstrate the potential use of SPRi for secretion-monitoring of pancreatic islets, small micro-organs that regulate glucose homeostasis in the body. In the islets, somatostatin works as a paracrine inhibitor of insulin and glucagon secretion. However, this inhibitory effect is lost in diabetic individuals and little is known about its contribution to the pathology of diabetes. Thus, the simultaneous detection of insulin, glucagon and somatostatin could help understand such communications. Previously, the authors introduced an SPRi biosensor to simultaneously monitor insulin, glucagon and somatostatin using an indirect competitive immunoassay. However, our sensor achieved a relatively high LOD for somatostatin detection (246 nM), the smallest of the three hormones. For this reason, the present work aimed to improve the performance of our SPRi biosensor using gold nanoparticles (GNPs) as a means of ensuring somatostatin detection from a small group of islets. Although GNP amplification is frequently reported in the literature for individual detection of analytes using SPR, studies regarding the optimal strategy in a multiplexed SPR setup are missing. Therefore, with the aim of finding the optimal GNP amplification strategies for multiplex sensing we compared three architectures: (1) GNPs immobilized on the sensor surface, (2) GNPs conjugated with primary antibodies (GNP-Ab1) and (3) GNPs conjugated with a secondary antibody (GNP-Ab2). Among these strategies an immunoassay using GNP-Ab2 conjugates was able to achieve multiplex detection of the three hormones without cross-reactivity and with 9-fold LOD improvement for insulin, 10-fold for glucagon and 200-fold for somatostatin when compared to the SPRi biosensor without GNPs. The present work denotes the first report of the simultaneous detection of such hormones with a sensitivity level comparable to ELISA assays, particularly for somatostatin.

On-chip 3D SERS materials produced by self-assemble of copper microparticle and galvanic replacement reaction

Surface-enhanced Raman scattering (SERS) has powerful capabilities in the field of environmental analysis and biological diagnostics because of its instinctive properties of high sensitivity and label-free detection. However, the fabrication of SERS substrate requires complicated processes and expensive equipment. This paper proposes a simple method approach to synthesize a 3D SERS substrate via electroless galvanic replacement reaction inside a microfluidic channel. Copper microparticles are assembled in a microfluidic channel, and silver nitrate solution is pumped into the channel to in situ produce the silver nanoparticles (Ag NPs) on the surface of copper microparticles. Because the copper particles occupy the channel by stack, the 3D Cu@AgNP SERS substrate can be obtained. The probing molecule (methylene blue) was utilized to investigate with the limit of detection (1×10^-7  M). The biological molecules (urea and melamine) have been used to demonstrate its benefits in medical applications, and cancer cell detection has been implemented to demonstrate its benefits in cell biology. In addition, the device can filter and wash cells, forming a simple and fast filter. Our work on this simple fabrication method of active SERS substrate has great value for medical and biological applications.

Quantitative and Specific Detection of Exosomal miRNAs for Accurate Diagnosis of Breast Cancer Using a Surface-Enhanced Raman Scattering Sensor Based on Plasmonic Head-Flocked Gold Nanopillars

MicroRNAs in exosomes (exosomal miRNAs) have attracted increased attention as cancer biomarkers for early diagnosis and prognosis owing to their stability in body fluids. Since strong association exists between exosomal miRNA expression levels and breast cancer, the development of effective methods that can monitor exosomal miRNA expression both over broad concentration ranges and in ultralow amounts is critical. Here, a surface-enhanced Raman scattering (SERS)-based sensing platform is developed for the quantitative determination of exosomal miRNAs. Ultrasensitive exosomal miRNA detection with single-nucleotide specificity is obtained from enhanced SERS signals from a uniform plasmonic head-flocked gold nanopillar substrate, which generates multiple hotspots and enables hybridization between short oligonucleotides, i.e., miRNAs and locked nucleic acid probes. The proposed SERS sensor shows an extremely low detection limit without any amplification process, a wide dynamic range (1 am to 100 nm), multiplex sensing capability and sound miRNA recovery in serum. Furthermore, this sensor allows reliable observation of exosomal miRNA expression patterns from breast cancer cell lines and can discriminate breast cancer subtype based on the difference between these patterns. The results suggest that this sensor can be used for universal cancer diagnosis and further biomedical applications through the quantitative measurement of exosomal miRNAs in bodily fluids.

A Nanoplasmonic Biosensor for Ultrasensitive Detection of Alzheimer's Disease Biomarker Using a Chaotropic Agent

Blood-based diagnosis (hemodiagnosis) of Alzheimer's disease (AD) is emerging as a promising alternative to cerebrospinal-fluid-based methods because blood contains various kinds of AD biomarkers, including amyloid beta 1-40, 1-42, and τ (tau) protein. However, with current technology, the accuracy of the blood-plasma-based methods is relatively low compared to the traditional methods because the concentration of AD biomarkers in blood plasma is incredibly low, and diverse interference is present in blood plasma, which hinders precise detection. Here, we suggest a nanoplasmonic biosensor using gold nanorods with a chaotropic agent for precise ultrasensitive detecting of Alzheimer's disease biomarkers in human plasma. This nanoplasmonic biosensor is based on the localized surface plasmon resonance (LSPR), which is extremely sensitive to the point where it can respond to an insignificant change of the refractive index around the gold nanoparticles. Also, using guanidine hydrochloride as a chaotropic agent, we can overcome the obstacles of blood-based AD diagnostics. In more detail, this agent interrupts the network between water molecules and weakens the hydrophobic interactions between proteins, remarkably improving detection capabilities to target τ protein. By reducing the overlapping ranges between protein levels in an age-matched control and AD patients' plasma, this system can accurately diagnose AD patients. This platform also can analyze disease from mild cognitive impairment using standardized blood biomarker tau protein, which is related to Alzheimer's disease. As a result, our platform can be applied to clinical trials, and thus it has excellent potential in the medical field.

Recent advances in merging photonic crystals and plasmonics for bioanalytical applications

Photonic crystals (PhCs) and plasmonic nanostructures offer the unprecedented capability to control the interaction of light and biomolecules at the nanoscale. Based on PhC and plasmonic phenomena, a variety of analytical techniques have been demonstrated and successfully implemented in many fields, such as biological sciences, clinical diagnosis, drug discovery, and environmental monitoring. During the past decades, PhC and plasmonic technologies have progressed in parallel with their pros and cons. The merging of photonic crystals with plasmonics will significantly improve biosensor performances and enlarge the linear detection range of analytical targets. Here, we review the state-of-the-art biosensors that combine PhC and plasmonic nanomaterials for quantitative analysis. The optical mechanisms of PhCs, plasmonic crystals, and metal nanoparticles (NPs) are presented, along with their integration and potential applications. By explaining the optical coupling of photonic crystals and plasmonics, the review manifests how PhC-plasmonic hybrid biosensors can achieve the advantages, including high sensitivity, low cost, and short assay time as well. The review also discusses the challenges and future opportunities in this fascinating field.

A label-free, ultra-highly sensitive and multiplexed SERS nanoplasmonic biosensor for miRNA detection using a head-flocked gold nanopillar

The combination of head-flocked gold nanopillars and sandwich DNA probes is an advanced label-free, ultra-high sensitive, multiplexed nanoplasmonic detection system of circulating miRNAs for cancer diagnosis and prognosis.

An ultrasensitive homogeneous aptasensor for carcinoembryonic antigen based on upconversion fluorescence resonance energy transfer

Carcinoembryonic antigen (CEA) has been recognized as one of the most important tumor markers. Herein, we reported an ultrasensitive homogeneous aptasensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and graphene oxide (GO) for CEA detection. The CEA aptamer modified UCNPs can bind to the surface of GO through π-π stacking interaction, resulting in fluorescence quenching due to the energy transfer from UCNPs to GO. After the introduction of CEA, the CEA aptamer preferentially combined with CEA to form three-dimensional structure which made UCNPs-aptamer dissociate from the GO, blocking the energy transfer process. The fluorescence of UCNPs was accordingly restored in a CEA concentration-dependent manner both aqueous solution and human serum samples. The aptasensor could monitor CEA level directly in human serum and the results were strongly correlated with commercial chemiluminescence kits. The excellent detection performance suggested promising prospect of the aptasensor in practical application.

Fiber Light-Coupled Optofluidic Waveguide (FLOW) Immunosensor for Highly Sensitive Detection of p53 Protein

Highly sensitive detection of molecular tumor markers is essential for biomarker-based cancer diagnostics. In this work, we showcase the implementation of fiber light-coupled optofluidic waveguide (FLOW) immunosensor for the detection of p53 protein, a typical tumor marker. The FLOW consists of a liquid-core capillary and an accompanying optical fiber, which allows evanescent interaction between light and microfluidic sample. Molecular binding at internal surface of the capillary induces a response in wavelength shift of the transmission spectrum in the optical fiber. To enable highly sensitive molecular detection, the evanescent-wave interaction has been strengthened by enlarging shape factor R via fine geometry control. The proposed FLOW immunosensor works with flowing microfluid, which increases the surface molecular coverage and improves the detection limit. As a result, the FLOW immunosensor presents a log-linear response to the tumor protein at concentrations ranging from 10 fg/mL up to 10 ng/mL. In addition, the nonspecifically adsorbed molecules can be effectively removed by the fluid at an optimal flow rate, which benefits the accuracy of the measurement. Tested in serum samples, the FLOW successfully maintains its sensitivity and specificity on p53 protein, making it suitable for diagnostics applications.

Bifunctional aptasensor based on novel two-dimensional nanocomposite of MoS2 quantum dots and g-C3N4 nanosheets decorated with chitosan-stabilized Au nanoparticles for selectively detecting prostate specific antigen

A novel nanostructured biosensing platform was designed based on two-dimensional (2D) nanocomposite of graphitic carbon nitride (g-C₃N₄) nanosheets and MoS₂ quantum dots (MoS₂ QDs), followed by decoration with chitosan-stabilized Au nanoparticles (CS-AuNPs) (denoted as MoS₂QDs@g-C₃N₄@CS-AuNPs), of which CS-AuNPs were prepared by plasma enhanced-chemical vapor deposition. Owning to the good surface plasmon performance of the CS-AuNPs and excellent electrochemical activity of MoS₂QDs@g-C₃N₄ nanosheets, the as-obtained 2D MoS₂QDs@g-C₃N₄@CS-AuNPs nanocomposite was simultaneously explored to construct both surface plasmon resonance spectroscopy (SPR) sensor and electrochemical aptasensor. The MoS₂QDs@g-C₃N₄@CS-AuNPs-based aptasensor shows strong bio-binding affinity toward the prostate specific antigen (PSA) targeted aptamer strands as compared to the individual component, including MoS₂ QDs, g-C₃N₄, and CS-AuNPs. When detecting PSA, the low limit of detection (LOD) of 0.71 pg mL^-1 deduced by electrochemical aptasensor is three orders of magnitude lower than that deduced by SPR sensor (0.77 ng mL^-1). As expected, both SPR sensor and electrochemical aptasensor demonstrate good selectivity, highly stability, acceptable reproducibility, and well consistent applicability in human serum. The satisfactory results suggest potential application of the MoS₂QDs@g-C₃N₄@CS-AuNPs in bifunctional biosensing fields and clinical monitoring of cancer markers.

Nanoplasmonic sensors for biointerfacial science

In recent years, nanoplasmonic sensors have become widely used for the label-free detection of biomolecules across medical, biotechnology, and environmental science applications. To date, many nanoplasmonic sensing strategies have been developed with outstanding measurement capabilities, enabling detection down to the single-molecule level. One of the most promising directions has been surface-based nanoplasmonic sensors, and the potential of such technologies is still emerging. Going beyond detection, surface-based nanoplasmonic sensors open the door to enhanced, quantitative measurement capabilities across the biointerfacial sciences by taking advantage of high surface sensitivity that pairs well with the size of medically important biomacromolecules and biological particulates such as viruses and exosomes. The goal of this review is to introduce the latest advances in nanoplasmonic sensors for the biointerfacial sciences, including ongoing development of nanoparticle and nanohole arrays for exploring different classes of biomacromolecules interacting at solid-liquid interfaces. The measurement principles for nanoplasmonic sensors based on utilizing the localized surface plasmon resonance (LSPR) and extraordinary optical transmission (EOT) phenomena are first introduced. The following sections are then categorized around different themes within the biointerfacial sciences, specifically protein binding and conformational changes, lipid membrane fabrication, membrane-protein interactions, exosome and virus detection and analysis, and probing nucleic acid conformations and binding interactions. Across these themes, we discuss the growing trend to utilize nanoplasmonic sensors for advanced measurement capabilities, including positional sensing, biomacromolecular conformation analysis, and real-time kinetic monitoring of complex biological interactions. Altogether, these advances highlight the rich potential of nanoplasmonic sensors and the future growth prospects of the community as a whole. With ongoing development of commercial nanoplasmonic sensors and analytical models to interpret corresponding measurement data in the context of biologically relevant interactions, there is significant opportunity to utilize nanoplasmonic sensing strategies for not only fundamental biointerfacial science, but also translational science applications related to clinical medicine and pharmaceutical drug development among countless possibilities.

A novel surface plasmon resonance biosensor based on the PDA-AgNPs-PDA-Au film sensing platform for horse IgG detection

Herein we report a novel polydopamine-silver nanoparticle-polydopamine-gold (PDA-AgNPs-PDA-Au) film based surface plasmon resonance (SPR) biosensor for horse IgG detection. The PDA-AgNPs-PDA-Au film sensing platform was built on Au-film via layer-by-layer self-assembly. Ag ion was reduced in situ to AgNPs in presence of PDA. The top PDA layer can prevent AgNPs from being oxidized and connect with antibody via Schiff alkali reaction directly. The morphology and thickness of the modified gold film were characterized using scanning electron microscope and Talystep. Experimental results show that the PDA-AgNPs-PDA-Au film sensing platform is stable, regenerative and sensitive for horse IgG detection. The detection limit of horse IgG obtained with the present biosensor is 0.625μgmL^-1, which is 2-fold and 4-fold lower than that obtained with biosensor based on PDA modified Au film and conventional biosensor based on MPA, respectively. Furthermore, when challenged to real serum samples, our sensor exhibited excellent specificity to horse IgG, suggesting its potential for industrial application.

Nanoplasmonic sensors for detecting circulating cancer biomarkers

The detection of cancer biomarkers represents an important aspect of cancer diagnosis and prognosis. Recently, the concept of liquid biopsy has been introduced whereby diagnosis and prognosis are performed by means of analyzing biological fluids obtained from patients to detect and quantify circulating cancer biomarkers. Unlike conventional biopsy whereby primary tumor cells are analyzed, liquid biopsy enables the detection of a wide variety of circulating cancer biomarkers, including microRNA (miRNA), circulating tumor DNA (ctDNA), proteins, exosomes and circulating tumor cells (CTCs). Among the various techniques that have been developed to detect circulating cancer biomarkers, nanoplasmonic sensors represent a promising measurement approach due to high sensitivity and specificity as well as ease of instrumentation and operation. In this review, we discuss the relevance and applicability of three different categories of nanoplasmonic sensing techniques, namely surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS), for the detection of different classes of circulating cancer biomarkers.

Multiplexing determination of cancer-associated biomarkers by surface-enhanced Raman scattering using ordered gold nanohoneycomb arrays

AIM

Here, a multiplex surface-enhanced Raman scattering (SERS) based assay for simultaneous quantitation of carcinoembryonic antigen (CEA) and α-fetoprotein (AFP) was developed.

METHODS

SERS tags of nanostars and SERS substrates of nanobowl arrays were functionalized with labeling and capturing antibodies, respectively. In presence of antigens, SERS tags, antigens and SERS substrates formed sandwich structure.

RESULTS

The SERS-based technique showed a wide linear range from 0.5 to 100 ng/ml and detection limits were 0.41 and 0.35 ng/ml for CEA and AFP in phosphate-buffered saline buffer, respectively. Analysis results of clinical serum samples using this technique were similar to that shown in phosphate-buffered saline buffer. The LODs were 0.44 and 0.40 ng/ml for CEA and AFP, respectively. Conclusion: The precision and stability of this analysis technique were satisfactory, meanwhile, no obvious cross-reactivity could be found. What's more, it also suggested that this novel multiplex SERS-based technique could be a simple, specific, reliable, sensitive and multiplexed tool for important diagnostic and prognostic applications.

Surface Plasmon Resonance or Biocompatibility-Key Properties for Determining the Applicability of Noble Metal Nanoparticles

Metal and in particular noble metal nanoparticles represent a very special class of materials which can be applied as prepared or as composite materials. In most of the cases, two main properties are exploited in a vast number of publications: biocompatibility and surface plasmon resonance (SPR). For instance, these two important properties are exploitable in plasmonic diagnostics, bioactive glasses/glass ceramics and catalysis. The most frequently applied noble metal nanoparticle that is universally applicable in all the previously mentioned research areas is gold, although in the case of bioactive glasses/glass ceramics, silver and copper nanoparticles are more frequently applied. The composite partners/supports/matrix/scaffolds for these nanoparticles can vary depending on the chosen application (biopolymers, semiconductor-based composites: TiO₂, WO₃, Bi₂WO₆, biomaterials: SiO₂ or P₂O₅-based glasses and glass ceramics, polymers: polyvinyl alcohol (PVA), Gelatin, polyethylene glycol (PEG), polylactic acid (PLA), etc.). The scientific works on these materials' applicability and the development of new approaches will be targeted in the present review, focusing in several cases on the functioning mechanism and on the role of the noble metal.