Label-Free Analysis of Multivalent Protein Binding Using Bioresponsive Nanogels and Surface Plasmon Resonance (SPR)

Developing New Peptides and Peptide-Drug Conjugates for Targeting the FGFR2 Receptor-Expressing Tumor Cells and 3D Spheroids

In this work, we utilized a biomimetic approach for targeting KATO (III) tumor cells and 3D tumoroids. Specifically, the binding interactions of the bioactive short peptide sequences ACSAG (A-pep) and LPHVLTPEAGAT (L-pep) with the fibroblast growth factor receptor (FGFR2) kinase domain was investigated for the first time. Both peptides have been shown to be derived from natural resources previously. We then created a new fusion trimer peptide ACSAG-LPHVLTPEAGAT-GASCA (Trimer-pep) and investigated its binding interactions with the FGFR2 kinase domain in order to target the fibroblast growth factor receptor 2 (FGFR2), which is many overexpressed in tumor cells. Molecular docking and molecular dynamics simulation studies revealed critical interactions with the activation loop, hinge and glycine-rich loop regions of the FGFR2 kinase domain. To develop these peptides for drug delivery, DOX (Doxorubicin) conjugates of the peptides were created. Furthermore, the binding of the peptides with the kinase domain was further confirmed through surface plasmon resonance studies. Cell studies with gastric cancer cells (KATO III) revealed that the conjugates and the peptides induced higher cytotoxicity in the tumor cells compared to normal cells. Following confirmation of cytotoxicity against tumor cells, the ability of the conjugates and the peptides to penetrate 3D spheroids was investigated by evaluating their permeation in co-cultured spheroids grown with KATO (III) and colon tumor-associated fibroblasts (CAFs). Results demonstrated that Trimer-pep conjugated with DOX showed the highest permeation, while the ACSAG conjugate also demonstrated reasonable permeation of the drug. These results indicate that these peptides may be further explored and potentially utilized to create drug conjugates for targeting tumor cells expressing FGFR2 for developing therapeutics.

Antibody-Conjugated Nanogel with Two Immune Checkpoint Inhibitors for Enhanced Cancer Immunotherapy

Cancer immunotherapy by immune checkpoint inhibitors (ICIs) acts on antitumor responses by stimulating the immune system to attack cancer cells. However, this powerful therapy is hampered by its high treatment cost and limited efficacy. Here, it is shown that the development of an antibody-conjugated nanogel (ANGel), consisting of N-isopropylacrylamide-co-acrylic acid and antibody-binding protein (protein A), potentiates the efficacy of two ICI monoclonal antibodies (mAbs) (cytotoxic-T-lymphocyte-associated antigen 4 and programmed death ligand-1 mAbs). Compared with mAb treatment alone, treatment with a bispecific ANGel surface-conjugated with the mAbs significantly decreases both the survival of Michigan Cancer Foundation-7 (MCF-7) and M D Anderson-Metastatic Breast-231 (MDA-MB-231) breast cancer cells in vitro and the burden of 4T1-luciferase-2-derived orthotopic syngeneic tumors in vivo. The bispecific ANGel is also more potent than the conventional treatment at prolonging survival in animals with triple-negative breast cancer. The advantage of the bispecific ANGel over other engineered bispecific antibodies arises not only from the adaptability to link multiple antibodies quickly and easily, but also from the capability to maintain the anticancer effect steadily at subcutaneously delivered tumor site. This finding has an important implication for cancer immunotherapy, opening a new paradigm to treat solid tumors.

Detection of α-Thrombin with Platelet Glycoprotein Ibα (GP1bα) for the Development of a Coagulation Marker

The detection of prothrombotic markers is crucial for understanding thromboembolism and assessing the effectiveness of anticoagulant drugs. α-Thrombin is a marker that plays a critical role in the coagulation cascade process. However, the detection of this enzymatic molecule was hindered by the absence of an efficient modality in the clinical environment. Previously, we reported that one α-thrombin interacts with two α-chains of glycoprotein Ib (GPIbα), i.e., multivalent protein binding (MPB), using bioresponsive hydrogel nanoparticles (nanogels) and optical microscopy. In this study, we demonstrated that GPIbα-mediated platforms led to the highly sensitive and quantitative detection of α-thrombin in various diagnostic systems. Initially, a bioresponsive nanogel-based surface plasmon resonance (nSPR) assay was developed that responds to the MPB of α-thrombin to GPIbα. The use of GPIbα for the detection of α-thrombin was further validated using the enzyme-linked immunosorbent assay, which is a gold-standard protein detection technique. Additionally, GPIbα-functionalized latex beads were developed to perform latex agglutination (LA) assays, which are widely used with hospital diagnostic instruments. Notably, the nSPR and LA assays exhibited a nearly 1000-fold improvement in sensitivity for α-thrombin detection compared to our previous optical microscopy method. The superiority of our GPIbα-mediated platforms lies in their stability for α-thrombin detection through protein-protein interactions. By contrast, assays relying on α-thrombin enzymatic activity using substrates face the challenge of a rapid decrease in postsample collection. These results suggested that the MPB of α-thrombin to GPIbα is an ideal mode for clinical α-thrombin detection, particularly in outpatient settings.

Polymeric Nanoparticles and Nanogels: How Do They Interact with Proteins?

Polymeric nanomaterials, nanogels, and solid nanoparticles can be fabricated using single or double emulsion methods. These materials hold great promise for various biomedical applications due to their biocompatibility, biodegradability, and their ability to control interactions with body fluids and cells. Despite the increasing use of nanoparticles in biomedicine and the plethora of publications on the topic, the biological behavior and efficacy of polymeric nanoparticles (PNPs) have not been as extensively studied as those of other nanoparticles. The gap between the potential of PNPs and their applications can mainly be attributed to the incomplete understanding of their biological identity. Under physiological conditions, such as specific temperatures and adequate protein concentrations, PNPs become coated with a "protein corona" (PC), rendering them potent tools for proteomics studies. In this review, we initially investigate the synthesis routes and chemical composition of conventional PNPs to better comprehend how they interact with proteins. Subsequently, we comprehensively explore the effects of material and biological parameters on the interactions between nanoparticles and proteins, encompassing reactions such as hydrophobic bonding and electrostatic interactions. Moreover, we delve into recent advances in PNP-based models that can be applied to nanoproteomics, discussing the new opportunities they offer for the clinical translation of nanoparticles and early prediction of diseases. By addressing these essential aspects, we aim to shed light on the potential of polymeric nanoparticles for biomedical applications and foster further research in this critical area.

Method for the Rapid Detection of SARS-CoV-2-Neutralizing Antibodies Using a Nanogel-Based Surface Plasmon Resonance Biosensor

The efficacy of coronavirus disease 2019 (COVID-19) vaccination is closely related to the serum levels of SARS-CoV-2-neutralizing antibodies (NAb) that bind to the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. Therefore, the rapid and quantitative measurement of SARS-CoV-2 NAb in the sera of vaccinated individuals is essential to develop an effective vaccine and further achieve population immunity, that is, herd immunity. The plaque reduction neutralization test, the gold standard for NAb effectiveness in serological tests, is accurate but requires biosafety level 3 facilities because of the use of the virus, which hampers its application in common laboratories and clinical practice. Here, we developed a bioresponsive nanogel-based surface plasmon resonance (nSPR) platform that detects SARS-CoV-2 NAb in clinical samples without complicated pretreatment. We found that multivalent protein binding (MPB) between the nanogel-conjugated RBD protein and SARS-CoV-2 NAb yields significantly enhanced SPR signals compared to the nonspecific interference from serum proteins in the nSPR assay. The excellence of our nanogel-based SARS-CoV-2 NAb test is due to its selectivity for NAb, with resistance to all other proteins, allowing the rapid detection and quantification of NAbs in each individual. Importantly, this nSPR assay provides a NAb detection platform for easier and safer COVID-19 vaccination strategies.

Tuning Surface Plasmon Resonance Responses through Size and Crosslinking Control of Multivalent Protein Binding-Capable Nanoscale Hydrogels

Surface plasmon resonance (SPR) phenomena have been widely studied to detect biomolecules because of their high sensitivity and ability to determine biomolecular interactions with kinetic information. However, highly selective detection in specific concentration ranges relevant to target biomolecules is still a challenging task. Recently, we developed bioresponsive nanoscale hydrogels to selectively intensify SPR signals through multivalent protein binding (MPB) events with target biomolecules, including IL-2, where we were able to demonstrate exceptional selectivity for target biomolecules with minimal responses to nonspecific and monovalent binding events. In this work, we systematically explored the relationship between the physical properties of MPB-capable nanoscale hydrogels and their SPR response induced in the presence of the programmed cell death protein 1 antibody (PD-1Ab) as a model target biomolecule. First, we developed a synthetic protocol by controlling various reaction parameters to construct a library of nanoscale poly(N-isopropylacrylamide-co-acrylic acid) hydrogels (NHs) with different sizes (from 400 nm to 1 μm) and degrees of crosslinking (from 2 to 8%). Then, by incorporating MPB-capable PD-1 receptors onto the surface of NHs to form PD-1-responsive nanoscale hydrogels (PNHs), the hydrogel size and crosslinking dependency of their SPR responses were investigated. Our results reveal the appropriate hydrogel size regime and degree of crosslinking for effective PD-1Ab detection at specific concentrations range between a few nM and 1 μM. Overall, our study demonstrates that by tuning the physical properties of the nanoscale hydrogel matrix, the sensitivity and detection range of MPB-based SPR sensors can be modulated to potentially benefit clinical applications such as monitoring diverse therapeutic biomolecules.

Plasmonic nanomaterials with responsive polymer hydrogels for sensing and actuation

Plasmonic nanomaterials have become an integral part of numerous technologies, where they provide important functionalities spanning from extraction and harvesting of light in thin film optical devices to probing of molecular species and their interactions on biochip surfaces. More recently, we witness increasing research efforts devoted to a new class of plasmonic nanomaterials that allow for on-demand tuning of their properties by combining metallic nanostructures and responsive hydrogels. This review addresses this recently emerged vibrant field, which holds potential to expand the spectrum of possible applications and deliver functions that cannot be achieved by separate research in each of the respective fields. It aims at providing an overview of key principles, design rules, and current implementations of both responsive hydrogels and metallic nanostructures. We discuss important aspects that capitalize on the combination of responsive polymer networks with plasmonic nanostructures to perform rapid mechanical actuation and actively controlled nanoscale confinement of light associated with resonant amplification of its intensity. The latest advances towards the implementation of such responsive plasmonic nanomaterials are presented, particularly covering the field of plasmonic biosensing that utilizes refractometric measurements as well as plasmon-enhanced optical spectroscopy readout, optically driven miniature soft actuators, and light-fueled micromachines operating in an environment resembling biological systems.

Label-free methods for optical in vitro characterization of protein-protein interactions

Protein-protein interactions are involved in the regulation and function of the majority of cellular processes. As a result, much effort has been aimed at the development of methodologies capable of quantifying protein-protein interactions, with label-free methods being of particular interest due to the associated simplified workflows and minimisation of label-induced perturbations. Here, we review recent advances in optical technologies providing label-free in vitro measurements of affinities and kinetics. We provide an overview and comparison of existing techniques and their principles, discussing advantages, limitations, and recent applications.

New Tool for Rapid and Accurate Detection of Interleukin-2 and Soluble Interleukin-2 Receptor α in Cancer Diagnosis Using a Bioresponsive Microgel and Multivalent Protein Binding

Interleukin-2 (IL-2) and its α receptor in soluble form (sIL-2Rα) are considered biomarkers for cancers and immune-related diseases. Enzyme-linked immunosorbent assay is the most common method used to evaluate biomarkers in clinical practice; it is precise but time-consuming and involves complicated procedures. Here, we have developed a rapid yet accurate modality for cancer diagnosis that enables on-site evaluation of cancer markers, that is, IL-2 and sIL-2Rα, without complicated pretreatment of cancer patient-derived blood samples. Surface plasmon resonance and bioresponsive microgels conjugated with IL-2 receptors, that is, IL-2Rβ and IL-2Rγ, were utilized to measure IL-2 and sIL-2Rα levels via multivalent protein binding (MPB) between the ligands and their receptors. Our results showed that this novel method enables us to perform cancer diagnosis with a 1000-fold dilution of serum in 10 min. The advantage of MPB-based cancer diagnosis originates from its great selectivity for a target molecule and tolerance to a myriad of nonspecific substances in serum, which allows on-site clinical evaluation. Importantly, our finding implies that MPB-based cancer diagnosis provides a new paradigm not only for improving cancer treatment but also for evaluating a target molecule in unpurified and complex solutions such as blood.

Novel Regeneration Approach for Creating Reusable FO-SPR Probes with NTA Surface Chemistry

To date, surface plasmon resonance (SPR) biosensors have been exploited in numerous different contexts while continuously pushing boundaries in terms of improved sensitivity, specificity, portability and reusability. The latter has attracted attention as a viable alternative to disposable biosensors, also offering prospects for rapid screening of biomolecules or biomolecular interactions. In this context here, we developed an approach to successfully regenerate a fiber-optic (FO)-SPR surface when utilizing cobalt (II)-nitrilotriacetic acid (NTA) surface chemistry. To achieve this, we tested multiple regeneration conditions that can disrupt the NTA chelate on a surface fully saturated with His6-tagged antibody fragments (scFv-33H1F7) over ten regeneration cycles. The best surface regeneration was obtained when combining 100 mM EDTA, 500 mM imidazole and 0.5% SDS at pH 8.0 for 1 min with shaking at 150 rpm followed by washing with 0.5 M NaOH for 3 min. The true versatility of the established approach was proven by regenerating the NTA surface for ten cycles with three other model system bioreceptors, different in their size and structure: His6-tagged SARS-CoV-2 spike fragment (receptor binding domain, RBD), a red fluorescent protein (RFP) and protein origami carrying 4 RFPs (Tet12SN-RRRR). Enabling the removal of His6-tagged bioreceptors from NTA surfaces in a fast and cost-effective manner can have broad applications, spanning from the development of biosensors and various biopharmaceutical analyses to the synthesis of novel biomaterials.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Matrix-specific mechanism of Fe ion release from laser-generated 3D-printable nanoparticle-polymer composites and their protein adsorption properties

Nanocomposites have been widely applied in medical device fabrication and tissue-engineering applications. In this context, the release of metal ions as well as protein adsorption capacity are hypothesized to be two key processes directing nanocomposite-cell interactions. The objective of this study is to understand the polymer-matrix effects on ion release kinetics and their relations with protein adsorption. Laser ablation in macromolecule solutions was employed for synthesizing Au and Fe nanoparticle-loaded nanocomposites based on thermoplastic polyurethane (TPU) and alginate. Confocal microscopy revealed a three-dimensional homogeneous dispersion of laser-generated nanoparticles in the polymer. The physicochemical properties revealed a pronounced dependence upon embedding of Fe and Au nanoparticles in both polymer matrices. Interestingly, the total Fe ion concentration released from alginate gels under static conditions decreased with increasing mass loadings, a phenomenon only found in the Fe-alginate system and not in the Cu/Zn-alginate and Fe-TPU control system (where the effects were proportioonal to the nanoparticle load). A detailed mechanistic examination of iron the ion release process revealed that it is probably not the redox potential of metals and diffusion of metal ions alone, but also the solubility of nano-metal oxides and affinity of metal ions for alginate that lead to the special release behaviors of iron ions from alginate gels. The amount of adsorbed bovine serum albumin (BSA) and collagen I on the surface of both the alginate and TPU composites was significantly increased in contrast to the unloaded control polymers and could be correlated with the concentration of released Fe ions and the porosity of composites, but was independent of the global surface charge. Interestingly, these effects were already highly pronounced at minute loadings with Fe nanoparticles down to 200 ppm. Moreover, the laser-generated Fe or Au nanoparticle-loaded alginate composites were shown to be a suitable bioink for 3D printing. These findings are potentially relevant for ion-sensitive bio-responses in cell differentiation, endothelisation, vascularisation, or wound healing.

Stimuli-responsive polymer/nanomaterial hybrids for sensing applications

Chemical and biological/biochemical sensors are capable of generating readout signals that are proportional to the concentration of specific analytes of interest. Signal sensitivity and limit of detection/quantitation can be enhanced through the use of polymers, nanomaterials, and their hybrids. Of particular interest are stimuli-responsive polymers and nanomaterials due to their ability to change their physical and/or chemical characteristics in response to their environment, and/or in the presence of molecular/biomolecular species of interest. Their individual use for sensing applications have many benefits, although this review focuses on the utility of stimuli-responsive polymer and nanomaterial hybrids. We discuss three main topics: stimuli-responsive nanogels, stimuli-responsive network polymers doped with nanomaterials, and nanoparticles modified with stimuli-responsive polymers.

Hydrogel Nanoparticle as a Functional Coating Layer in Biosensing, Tissue Engineering, and Drug Delivery

The development of functional coating materials has resulted in many breakthroughs in the discovery of energy, environmental, and biomedical applications. Responsive polymeric hydrogels are an example of smart coating materials due to their stimuli-responsive characteristics upon changes in their local environment. This review focuses on the introduction of hydrogel nanoparticles and their applications in functional layers as responsive coating materials. Hydrogels are explained by the composition of cross-links and monomers used for preparation. In particular, an important class of responsive hydrogels, that is, nanosized hydrogel particles (nanogels), are described for thee synthesis, modification, and application in assembly of functional coating layers. Finally, nanogel functional layers for biological applications will be discussed with recent advances in biosensing, tissue engineering, and drug delivery.

Tag-Free Methodology for Ultrasensitive Biosensing of miRNA Based on Intrinsic Isotope Detection

MicroRNA (miRNA), of which the abnormal intracellular expression highly associates with numerous pathological diseases, is considered as an important biomarker for early diagnosis and state monitoring of cancer. To avoid the tedious and vunerable labeling process, a series of novel label-free quantification methods for miRNA have been proposed. However, current label-free miRNA assays still require the presynthesis of a sensing unit as tags. Herein, we propose a "tag-free" methodology for miRNA quantification to realize the removal of sensing labels. Combining a concatenated-HCR (C-HCR) strategy and high-resolution inductive couple plasma mass spectrometry (HR-ICPMS) detection, we utilize phosphorus as a characteristic element to quantify the concentration of nucleotides. Benefiting from the excellent amplification performance of C-HCR and element analysis capacity of HR-ICPMS, a 13 fM limit of detection (LOD) was obtained. Ulteriorly, we verify the anti-interference performance of the proposed tag-free miRNA assay with a phosphate substrate-contained cell culture medium or nontarget miRNA. Furthermore, two cell lines of human cancer were chosen to evaluate the real biological sample analysis capacity. The good correlation data indicate promising prospects of the proposed tag-free methodology for the quantification of miRNA in tumor cells and further clinical applications.