Multivalent Antibody-Nanoparticle Conjugates To Enhance the Sensitivity of Surface-Enhanced Raman Scattering-Based Immunoassays

Surface-Enhanced Raman Spectroscopy for Biomedical Applications: Recent Advances and Future Challenges

The year 2024 marks the 50th anniversary of the discovery of surface-enhanced Raman spectroscopy (SERS). Over recent years, SERS has experienced rapid development and became a critical tool in biomedicine with its unparalleled sensitivity and molecular specificity. This review summarizes the advancements and challenges in SERS substrates, nanotags, instrumentation, and spectral analysis for biomedical applications. We highlight the key developments in colloidal and solid SERS substrates, with an emphasis on surface chemistry, hotspot design, and 3D hydrogel plasmonic architectures. Additionally, we introduce recent innovations in SERS nanotags, including those with interior gaps, orthogonal Raman reporters, and near-infrared-II-responsive properties, along with biomimetic coatings. Emerging technologies such as optical tweezers, plasmonic nanopores, and wearable sensors have expanded SERS capabilities for single-cell and single-molecule analysis. Advances in spectral analysis, including signal digitalization, denoising, and deep learning algorithms, have improved the quantification of complex biological data. Finally, this review discusses SERS biomedical applications in nucleic acid detection, protein characterization, metabolite analysis, single-cell monitoring, and in vivo deep Raman spectroscopy, emphasizing its potential for liquid biopsy, metabolic phenotyping, and extracellular vesicle diagnostics. The review concludes with a perspective on clinical translation of SERS, addressing commercialization potentials and the challenges in deep tissue in vivo sensing and imaging.

Expression-Dependent Tumor Pretargeting via Engineered Avidity

Selective delivery of therapeutic modalities to tumor cells via binding of tumor-selective cell-surface biomarkers has empowered substantial advances in cancer treatment. Yet, tumor cells generally lack a truly specific biomarker that is present in high density on tumor tissue while being completely absent from healthy tissue. Rather, low but nonzero expression in healthy tissues results in on-target, off-tumor activity with detrimental side effects that constrain the therapeutic window or prevent use altogether. Advanced technologies to enhance the selectivity for tumor targeting are sorely needed. We have engineered a binding platform that is quantitatively dependent upon expression levels, via avidity-driven specificity, rather than binarily reliant on the presence or absence of a biomarker. We systematically varied monomeric binding affinity by engineering affibodies to target carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) and folate receptor 1 (FolR1). Two identical affibody ligands were tethered, with varying polypeptide linker lengths, to a nanobody that binds Alfa peptide to create a bispecific, trivalent protein for use in pretargeted radioligand therapy. Expression-dependent targeting was achieved in both systems: with 110 nM monomeric affinity to CEACAM5 with a two-amino-acid linker or with 250 nM monomeric affinity for FolR1 and a 10 amino acid linker. The latter bispecific, trivalent achieved over 25-fold differentiation between FolR1high and FolR1low cells in a mixed culture. Similar selectivity was achieved in a size-efficient bivalent molecule lacking a central nanobody. Moreover, the avid bivalent affibody molecule exhibited minimal inhibition by soluble antigen, whereas high-affinity bivalent antibody was inhibited by 97 ± 2%, which is indicative of serum inhibition of shed antigen. This work advances design principles for achieving expression-dependent tumor targeting via low-affinity, high-avidity ligands.

Anti-PD-L1 Antibody Fragment Linked to Tumor-Targeting Lipid Nanoparticle Can Eliminate Cancer and Its Metastasis via Photoimmunotherapy

Effective cancer therapy aims to treat primary tumors and metastatic and recurrent cancer. Immune checkpoint blockade-mediated immunotherapy has shown promising effects against tumors; however, its efficacy in metastatic or recurrent cancer is limited. Here, based on the advantages of nanomedicine, lipid nanoparticles (LNPs) that can target tumors are synthesized for photothermal therapy (PTT) and immunotherapy to treat primary and metastatic recurrent cancer. These LNPs, termed piLNPs, are encapsulated with indocyanine green and incorporated with the antigen (Ag)-binding fragment of the anti-PD-L1 antibody for targeting tumors and immunotherapy. Intravenously injected piLNPs in 4T1 breast tumor-bearing BALB/c mice effectively target the 4T1 tumor and are suitable for performing PTT using a near-infrared laser. Moreover, lung metastatic 4T1 tumor growth is completely prevented in mice previously cured of the 4T1 breast tumor by piLNP treatment and rechallenged with lung 4T1 metastatic cancer. Blockage of the second challenged metastatic 4T1 breast cancer by piLNP is due to the activation of Ag-specific T cells. Cytotoxic T lymphocytes from piLNP-cured mice selectively attack 4T1 breast cancer cells. Therefore, piLNP can be used as a multifunctional breast cancer treatment composition that can target tumors, treat primary tumors, and prevent metastasis and recurrence.

Biomolecule-functionalized nanoformulations for prostate cancer theranostics

BACKGROUND

Even with the advancement in the areas of cancer nanotechnology, prostate cancer still poses a major threat to men's health. Nanomaterials and nanomaterial-derived theranostic systems have been explored for diagnosis, imaging, and therapy for different types of cancer still, for prostate cancer they have not delivered at full potential because of the limitations like in vivo biocompatibility, immune responses, precise targetability, and therapeutic outcome associated with the nanostructured system.

AIM OF REVIEW

Functionalizing nanomaterials with different biomolecules and bioactive agents provides advantages like specificity towards cancerous tumors, improved circulation time, and modulation of the immune response leading to early diagnosis and targeted delivery of cargo at the site of action.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this review, we have emphasized the classification and comparison of various nanomaterials based on biofunctionalization strategy and source of biomolecules such that it can be used for possible translation in clinical settings and future developments. This review highlighted the opportunities for embedding highly specific biological targeting moieties (antibody, aptamer, oligonucleotides, biopolymer, peptides, etc.) on nanoparticles which can improve the detection of prostate cancer-associated biomarkers at a very low limit of detection, direct visualization of prostate tumors and lastly for its therapy. Lastly, special emphasis was given to biomimetic nanomaterials which include functionalization with extracellular vesicles, exosomes and viral particles and their application for prostate cancer early detection and drug delivery. The present review paves a new pathway for next-generation biofunctionalized nanomaterials for prostate cancer theranostic application and their possibility in clinical translation.

Recent development of surface-enhanced Raman scattering for biosensing

Surface-Enhanced Raman Scattering (SERS) technology, as a powerful tool to identify molecular species by collecting molecular spectral signals at the single-molecule level, has achieved substantial progresses in the fields of environmental science, medical diagnosis, food safety, and biological analysis. As deepening research is delved into SERS sensing, more and more high-performance or multifunctional SERS substrate materials emerge, which are expected to push Raman sensing into more application fields. Especially in the field of biological analysis, intrinsic and extrinsic SERS sensing schemes have been widely used and explored due to their fast, sensitive and reliable advantages. Herein, recent developments of SERS substrates and their applications in biomolecular detection (SARS-CoV-2 virus, tumor etc.), biological imaging and pesticide detection are summarized. The SERS concepts (including its basic theory and sensing mechanism) and the important strategies (extending from nanomaterials with tunable shapes and nanostructures to surface bio-functionalization by modifying affinity groups or specific biomolecules) for improving SERS biosensing performance are comprehensively discussed. For data analysis and identification, the applications of machine learning methods and software acquisition sources in SERS biosensing and diagnosing are discussed in detail. In conclusion, the challenges and perspectives of SERS biosensing in the future are presented.

Reagents for Mass Cytometry

Mass cytometry (cytometry by time-of-flight detection [CyTOF]) is a bioanalytical technique that enables the identification and quantification of diverse features of cellular systems with single-cell resolution. In suspension mass cytometry, cells are stained with stable heavy-atom isotope-tagged reagents, and then the cells are nebulized into an inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) instrument. In imaging mass cytometry, a pulsed laser is used to ablate ca. 1 μm² spots of a tissue section. The plume is then transferred to the CyTOF, generating an image of biomarker expression. Similar measurements are possible with multiplexed ion bean imaging (MIBI). The unit mass resolution of the ICP-TOF-MS detector allows for multiparametric analysis of (in principle) up to 130 different parameters. Currently available reagents, however, allow simultaneous measurement of up to 50 biomarkers. As new reagents are developed, the scope of information that can be obtained by mass cytometry continues to increase, particularly due to the development of new small molecule reagents which enable monitoring of active biochemistry at the cellular level. This review summarizes the history and current state of mass cytometry reagent development and elaborates on areas where there is a need for new reagents. Additionally, this review provides guidelines on how new reagents should be tested and how the data should be presented to make them most meaningful to the mass cytometry user community.

Targeted Immuno-Antiretroviral to Promote Dual Protection against HIV: A Proof-of-Concept Study

The C-C motif chemokine receptor-5 (CCR5) expression on the T-cell surface is the prime barrier to HIV/AIDS eradication, as it promotes both active human immunodeficiency virus (HIV)-infection and latency; however, antiretrovirals (ARVs) suppress plasma viral loads to non-detectable levels. Keeping this in mind, we strategically designed a targeted ARVs-loaded nanoformulation that targets CCR5 expressing T-cells (e.g., CD4+ cells). Conceptually, CCR5-blocking and targeted ARV delivery would be a dual protection strategy to prevent HIV infection. For targeting CCR5+ T-cells, the nanoformulation was surface conjugated with anti-CCR5 monoclonal antibodies (CCR5 mAb) and loaded with dolutegravir+tenofovir alafenamide (D+T) ARVs to block HIV replication. The result demonstrated that the targeted-ARV nanoparticle's multimeric CCR5 binding property improved its antigen-binding affinity, prolonged receptor binding, and ARV intracellular retention. Further, nanoformulation demonstrated high binding affinity to CCR5 expressing CD4+ cells, monocytes, and other CCR5+ T-cells. Finally, the short-term pre-exposure prophylaxis study demonstrated that prolonged CCR5 blockage and ARV presence further induced a "protective immune phenotype" with a boosted T-helper (Th), temporary memory (TM), and effector (E) sub-population. The proof-of-concept study that the targeted-ARV nanoformulation dual-action mechanism could provide a multifactorial solution toward achieving HIV "functional cure."

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Development of 6E3 antibody-mediated SERS immunoassay for drug-resistant influenza virus

Influenza viruses are responsible for several pandemics and seasonal epidemics and pose a major public health threat. Even after a major outbreak, the emergence of drug-resistant influenza viruses can pose disease control problems. Here we report a novel 6E3 monoclonal antibody capable of recognizing and binding to the H275Y neuraminidase (NA) mutation, which has been associated with reduced susceptibility of influenza viruses to NA inhibitors. The 6E3 antibody had a K_D of 72.74 μM for wild-type NA and 32.76 pM for H275Y NA, suggesting that it can identify drug-resistant pandemic H1N1 (pH1N1) influenza virus. Molecular modeling studies also suggest the high-affinity binding of this antibody to pH1N1 H275Y NA. This antibody was also subject to dot-blot, enzyme-linked immunosorbent assay, bare-eye detection, and lateral flow assay to demonstrate its specificity to drug-resistant pH1N1. Furthermore, it was immobilized on Au nanoplate and nanoparticles, enabling surface-enhanced Raman scattering (SERS)-based detection of the H275Y mutant pH1N1. Using 6E3 antibody-mediated SERS immunoassay, the drug-resistant influenza virus can be detected at a low concentration of 10² plaque-forming units/mL. We also detected pH1N1 in human nasopharyngeal aspirate samples, suggesting that the 6E3-mediated SERS assay has the potential for diagnostic application. We anticipate that this newly developed antibody and SERS-based immunoassay will contribute to the diagnosis of drug-resistant influenza viruses and improve treatment strategies for influenza patients.

Advances in Antibody Preparation Techniques for Immunoassays of Total Aflatoxin in Food

Aflatoxin (AF) contamination is a major concern in the food and feed industry because of its prevalence and toxicity. Improved aflatoxin detection methods are still needed. Immunoassays are an important method for total aflatoxin (TAF) analysis in food due to its technical advantages such as high specificity, sensitivity, and simplicity, but require high-quality antibodies. Here, we first review the three ways to prepare high-quality antibodies for TAF immunoassay, second, compare the advantages and disadvantages of antigen synthesis methods for B-group and G-group aflatoxins, and third, describe the status of novel genetic engineering antibodies. This review can provide new methods and ideas for the development of TAF immunoassays.

Troponin Aptamer on an Atomically Flat Au Nanoplate Platform for Detection of Cardiac Troponin I

Well-ordered bioreceptors on atomically flat Au surfaces can be a high-performance biosensor. Cardiac troponin I proteins (cTnIs) have been regarded as a specific biomarker for acute myocardial infarction (AMI). Here, we report the accurate detection of cTnIs using an aptamer-immobilized Au nanoplate platform. The single-crystalline and atomically flat Au nanoplate was characterized by atomic force microscopy. For the precise detection of cTnI, we immobilized an aptamer that can strongly bind to cTnI onto an atomically flat Au nanoplate. Using the aptamer-immobilized Au nanoplate, cTnIs were successfully detected at a concentration of 100 aM (2.4 fg/mL) in buffer solution. Furthermore, cTnIs in serum could be identified at a concentration of 100 fM (2.4 pg/mL). The total assay time was ~7 h. Importantly, the aptamer-immobilized Au nanoplate enabled us to diagnose AMI patients accurately, suggesting the potential of the present method in the diagnosis of AMI.

Novel Chemiluminescence Sensor for Thrombin Detection Based on Dual-Aptamer Biorecognition and Mesoporous Silica Encapsulated with Iron Porphyrin

Thrombin is a marker of blood-related diseases, and its detection is of great significance in the fields of medical and biological research. Herein, a novel chemiluminescence (CL) sensor for thrombin detection was prepared based on dual-aptamer biorecognition and mesoporous silica encapsulated with iron porphyrin. Mesoporous silica encapsulated with hematin by aptamer1 (Apt1/hematin/M-SiO₂) and magnetic microspheres modified with aptamer2 (Apt2/NH₂-MS) were successfully prepared, and the two materials were used to construct a CL sensor to detect thrombin. Primarily, Apt2/NH₂-MS is used for pretreatment separation of thrombin samples by the biorecognition effect between the aptamer (Apt2) and target (thrombin). Then, thrombin/Apt2/NH₂-MS is again recognized with Apt1 on the surface of Apt1/hematin/M-SiO₂ and Apt1/thrombin/Apt2/NH₂-MS is formed, so dual-aptamer biorecognition is realized. Meanwhile, the generated Apt1/thrombin/Apt2/NH₂-MS makes Apt1 shed off the surface of M-SiO₂ and release hematin. The released hematin can catalyze the luminol-H₂O₂ CL reaction. Therefore, a sandwich-type CL sensor was constructed based on dual-aptamer biorecognition and hematin catalysis for the detection of thrombin. The sensor has a linear range of 7.5 × 10^-15 to 2.5 × 10^-10 mol·L^-1 and a detection limit of 2.2 × 10^-15 mol·L^-1 and also exhibits excellent selectivity, reproducibility, and stability. The sensor was successfully used for the detection of thrombin in serum samples, which makes it possible to apply the sensor in the detection of thrombin in actual samples.

Recent advances in nanomaterial-enhanced enzyme-linked immunosorbent assays

This review highlights functional roles of nanomaterials for advancing conventional ELISA assays by serving as substrate-alternatives, enzyme-alternatives, or non-enzyme amplifiers.

Atomically Flat Au Nanoplate Platforms Enable Ultraspecific Attomolar Detection of Protein Biomarkers

Atomically flat surfaces of single-crystalline Au nanoplates can maximize the functionality of biomolecules, thus realizing extremely high-performance biosensors. Here, we report both highly specific and supersensitive detection of C-reactive protein (CRP) by employing atomically flat Au nanoplates. CRP is a protein biomarker for inflammation and infection and can be used as a predictive or prognostic marker for various cardiovascular diseases. To maximize the binding capacity for CRP, we carefully optimized the Au nanoplate-Cys3-protein G-anti-CRP structure by observing atomic force microscopy (AFM) images. The optimally anti-CRP-immobilized Au nanoplates allowed extremely specific detection of CRP at the attomolar level. To confirm the binding of CRP onto the Au nanoplate, we assembled Au nanoparticles (NPs) onto the CRP-captured Au nanoplate by sandwich immunoreaction and obtained surface-enhanced Raman scattering (SERS) spectra and scanning electron microscopy (SEM) images. Both the SERS and SEM results showed that we completely eliminated the nonspecific binding of Au NPs onto the optimally anti-CRP-immobilized Au nanoplate. Compared with the anti-CRP-immobilized rough Au film and the randomly anti-CRP-attached Au nanoplate, the optimally anti-CRP-immobilized Au nanoplate provided a highly improved detection limit of 10^-17 M. In this study, it was validated that ultraclean and ultraflat Au nanoplates can maximize the sensing capability of CRP. We expect that these Au nanoplates will enable the feasible detection of many important biomarkers with high specificity and high sensitivity.