Carboxyl functionalized gold nanorods for sensitive visual detection of biomolecules

Multiplexed immunolabelling of cancer using bioconjugated plasmonic gold-silver alloy nanoparticles

Reliable protein detection methods are vital for advancing biological research and medical diagnostics. While immunohistochemistry and immunofluorescence are commonly employed, their limitations underscore the necessity for alternative approaches. This study introduces immunoplasmonic labelling, utilizing plasmonic nanoparticles (NPs), specifically designed gold and gold-silver alloy NPs (Au:Ag NPs), for multiplexed and quantitative protein detection. These NPs, when coupled with antibodies targeting proteins of interest, enable accurate counting and evaluation of protein expression levels while overcoming issues such as autofluorescence. In this study, we compare two nanoparticle functionalization strategies-one coating based on thiolated PEG and one coating based on calix[4]arenes-on gold and gold-silver alloy nanoparticles of varying sizes. Overall results tend to demonstrate a greater versatility for the calix[4]arene-based coating. With this coating and using the classical EDC/sulfo-NHS cross-linking procedure, we also demonstrate the successful multiplexed immunolabelling of Her2, CD44, and EpCAM in breast cancer cell lines (SK-BR-3 and MDA-MB-231). Furthermore, we introduce a user-friendly software for automatic NP detection and classification by colour, providing a promising proof-of-concept for the practical application of immunoplasmonic techniques in the quantitative analysis of biopsies in the clinical setting.

Chitosan-initiated gold nanoparticles with enhanced fluorescence for unique Fe3+/PPi sensing and photothermal therapy

The design of surface ligands is crucial for ligand-protected gold nanoparticles (AuNPs). Herein, following the principle of green synthesis, environmentally friendly gold nanoparticles (AuNPs@His@CC, AuHC) were fabricated based on dual ligands of histidine and carboxylated chitosan. AuHC showed the advantages of low toxicity, good photoluminescent stability and ideal biocompatibility. Compared with single histidine-coated gold nanoclusters (AuNCs@His, AuH), AuHC presented enhanced fluorescence attributed to the addition of chitosan. The blue-emitting AuHC has a unique response to Fe3+ with detection limits as low as 9.51 nM. Interestingly, the quenched fluorescence of AuHC-Fe3+ system could be restored through the introduction of PPi with a detection limit of 10.6 μM. So an "on-off-on" fluorescence sensing platform was achieved. Apart from good optical properties and sensing, the designed AuHC demonstrated outstanding photothermal conversion efficiency (27.8 %), which made it ideal material for thermal ablation of tumor. To be specific, after laser irradiation (660 nm, 0.78 W cm-2, 10 min) of AuHC, the survival rate of HeLa cells as a tumor cell model decreased to 12.7 %, indicating that AuHC has a significant tumor inhibition effect in vitro. Besides, AuHC also could be a befitting candidate for overcoming drug-resistant tumor cells such as MCF-7/ADR cells. Notably, AuHC can markedly ablate solid tumors in 4T1 tumor-bearing mice after laser irradiation (660 nm, 0.78 W cm-2, 10 min). Hence this work provides insight into the design of multifunctional AuNPs platform for simultaneously integrating the ion sensing and photothermal therapy of cancer.

Progress of Mesoporous Silica Coated Gold Nanorods for Biological Imaging and Cancer Therapy

For unique surface plasmon absorption and fluorescence characteristics, gold nanorods have been developed and widely employed in the biomedical field. However, limitations still exist due their low specific surface area, instability and tendency agglomerate in cytoplasm. Mesoporous silica materials have been broadly applied in field of catalysts, adsorbents, nanoreactors, and drug carriers due to its unique mesoporous structure, highly comparative surface area, good stability and biocompatibility. Therefore, coating gold nanorods with a dendritic mesopore channels can effectively prevent particle agglomeration, while increasing the specific surface area and drug loading efficiency. This review discusses the advancements of GNR@MSN in synthetic process, bio-imaging technique and tumor therapy. Additionally, the further application of GNR@MSN in imaging-guided treatment modalities is explored, while its promising superior application prospect is highlighted. Finally, the issues related to in vivo studies are critically examined for facilitating the transition of this promising nanoplatform into clinical trials.

Significance of the antibody orientation for the lateral flow immunoassays: A mini-review

Lateral flow immunoassays (LFIAs) are well-established and broadly commercialized tools in the field of point-of-care testing due to their simplicity, rapidity, cost-effectiveness, and low requirements for users and equipment. However, the insensitivity and the possibility of producing inaccurate results associated with conventional LFIAs have impeded their wide-ranging implementation, especially for monitoring ultra-trace level of analytes. Moreover, the heterogeneous distribution of amino acids on the surface of antibody (Ab) results in a lack of precise control over their orientation, which ultimately leads to unsatisfactory detection performance. To address those concerns, herein we provide an overview of the emerging efforts to prepare well-established LFIAs from the perspective of orientation manipulation of immobilized Abs on the nanoprobes or membranes. The preparation of excellent nanoprobes with Abs being oriented immobilized, consisting of the nanoprobe types, Ab types, and their conjugation chemistries, are reviewed. Followed by the introduction of efforts highlight the importance of directionally immobilized Ab on the membrane. The effects of Ab orientation on the analytical performance of LFIA platforms in terms of sensitivity, specificity, rapidity, reliability, cost-effectiveness, and stability are also summarized. Finally, the future development and challenges of Ab-oriented immobilization-assisted LFIAs are also discussed.

Hot-Electron Dynamics Mediated Medical Diagnosis and Therapy

Surface plasmon resonance excitation significantly enhances the absorption of light and increases the generation of "hot" electrons, i.e., conducting electrons that are raised from their steady states to excited states. These excited electrons rapidly decay and equilibrate via radiative and nonradiative damping over several hundred femtoseconds. During the hot-electron dynamics, from their generation to the ultimate nonradiative decay, the electromagnetic field enhancement, hot electron density increase, and local heating effect are sequentially induced. Over the past decade, these physical phenomena have attracted considerable attention in the biomedical field, e.g., the rapid and accurate identification of biomolecules, precise synthesis and release of drugs, and elimination of tumors. This review highlights the recent developments in the application of hot-electron dynamics in medical diagnosis and therapy, particularly fully integrated device techniques with good application prospects. In addition, we discuss the latest experimental and theoretical studies of underlying mechanisms. From a practical standpoint, the pioneering modeling analyses and quantitative measurements in the extreme near field are summarized to illustrate the quantification of hot-electron dynamics. Finally, the prospects and remaining challenges associated with biomedical engineering based on hot-electron dynamics are presented.

Dual enzyme induced colorimetric sensor for simultaneous identifying multiple pathogens

Rapid and accurate identification of foodborne pathogens improves public health. Currently employed methods are time-consuming, sensitive to environmental factors, and complex. This study develops a colorimetric sensor for detecting multiple bacteria with one probe using double-enzyme-induced colorimetry. Based on alkaline phosphatase (ALP) in bacteria decomposes L-ascorbic acid 2-magnesium phosphate salt hydrate into ascorbic acid (AA). Manganese dioxide flowers (MnO₂ NFs) can oxidize TMB to etch gold nanorods (Au NRs), which can be inhibited by AA reduction to produce rich colors. Bacteria with varying ALP levels can be identified based on color changes and plasmon resonance wavelength signals produced from Au NRs. Furthermore, the conversion of RGB signals to digital signals and the use of linear discriminant analysis (LDA) allowed 99.57% accuracy in identifying multiple bacteria. It can simultaneously identify five foodborne pathogens across diverse environments (shrimp, meat, milk, etc.). This method may be useful for the rapid and simple identification of foodborne illnesses.

A novel detection strategy for nitrofuran metabolite residues: Dual-mode competitive-type electrochemical immunosensor based on polyethyleneimine reduced graphene oxide/gold nanorods nanocomposite and silica-based multifunctional immunoprobe

Excessive residues of semicarbazide (SEM) can accumulate in animals after the original drug has been abused, posing a risk to human health. Herein, based on multifunctional silica-initiated dual mode signal response, a novel competitive-type immunosensor was constructed for ultrasensitive detection of SEM. As a preliminary signal amplification platform for immunosensors, polyethyleneimine reduced graphene oxide composite gold nanorods (PEI-rGO/AuNRs) modified gold electrodes (AuE) provide a high specific surface area and high electrical conductivity. The thionine-aminated silica nanospheres-AuPt (thi-SiO₂@AuPt) were synthesized by a racile coprecipitation method for enzyme immobilization and redox species loading. The multifunctional silica nanosphere conjugated with labeling antibodies (Ab₂) was employed as an immunoprobe. The per unit concentration target of SEM can be determined by differential pulse voltammetry (DPV) to detect the thi loaded on the immunoprobe, which can also be determined by square wave voltammetry (SWV) to detect the current generated by the reaction system of H₂O₂ and hydroquinone (HQ) catalyzed by the immunoprobe with peroxidase. Under optimal conditions, the proposed immunosensor displayed a wide linear range from 1 μg-0.01 ng/mL and low detection limits (S/N = 3) of 0.488 pg/mL and 0.0157 ng/mL, respectively. Ultimately, the developed method exhibits excellent performance in practical applications, providing promising probabilities for SEM detection.

Microfluidic fluorescent platform for rapid and visual detection of veterinary drugs

The overuse of veterinary drugs and veterinary drug residues is increasingly becoming an obstacle to sustainable development worldwide. It is therefore imperative to establish a quantitative, sensitive and efficient method for the detection of veterinary drugs. Herein, we developed a visual microfluidic detection platform for rapid and sensitive detection of veterinary drugs using CdTe quantum dots (QDs) with three different ligands as the sensing units. Green-emissive 3-mercaptopropionic acid (MPA)-CdTe QDs, yellow-emissive thioglycolic acid (TGA)-CdTe QDs and orange-emissive N-acetyl-l-cysteine (NAC)-CdTe QDs were synthesized by a sulfhydryl aqueous phase method. These CdTe QDs show selective rapid fluorescence response to pefloxacin (PEF), malachite green (MG), and 1-aminohydantoin hydrochloride (AHD). With the concentration of veterinary drugs increasing, the CdTe QDs reveals a fluorescence color variation from bright to dark until quenched and the response degree of CdTe QDs with different ligands to veterinary drugs is different. Specifically, the limits of detection (LODs) of MPA-CdTe, TGA-CdTe and NAC-CdTe QDs probes for PEF were 7.57 μM, 1.75 μM and 2.90 μM, respectively, and the response was complete in a few seconds, realizing the sensitive and rapid detection of PEF. The three kinds of CdTe QDs could also be used in the detection of other veterinary drugs such as MG and AHD. Finally, a microfluidic detection platform was constructed for visual sensing and rapid detection towards veterinary drugs. The sensor platform holds the advantages of simple operation, low cost, rapid sensing and good sensitivity, and is potentially useful for visual quantitative detection of veterinary drug residues in aquatic products and the environment.

Ready-to-use room temperature one-pot synthesis of surface-decorated gold nanoparticles with targeting attributes

Gold nanoparticles (AuNPs) can be used in diagnostic and therapeutic applications. The development of facile and fast synthetic approaches is accordingly desirable towards ready-to-use biomedical materials. We report a practical one-pot method for the synthesis in aqueous media and room temperature of surface-decorated AuNPs with enhanced biological responses. The gold ions could be reduced using only polyethyleneimine (PEI) derivatives containing sugar and-or alkyl chains acting simultaneously as reducing and stabilizing agent, without the aid of any other mediator. The process is possibly potentialized by the presence of the amino groups in the polymer chains which further confer colloidal stability. The kinetics of AuNPs nucleation and growth depends on the chemical nature of the polymer chains. Particularly, the presence of lactose moieties conjugated to the PEI chains conducted to surface-decorated AuNPs with low cytotoxicity that are remarkably faster uptaken by HepG2 cells. These cells overexpress asialoglycoprotein (ASGP-R), a galactose receptor. These findings may kick off significant advances towards the practical and ready-to-use manufacturing of functionalized AuNPs towards cell-targeting since the methodology is applicable for a large variety of other ligands that can be conjugated to the same polymer chains.

The effect of layer thickness and immobilization chemistry on the detection of CRP in LSPR assays

The immobilization of a capture molecule represents a crucial step for effective usage of gold nanoparticles in localized surface plasmon resonance (LSPR)-based bioanalytics. Depending on the immobilization method used, the resulting capture layer is of varying thickness. Thus, the target binding event takes place at different distances to the gold surface. Using the example of a C-reactive protein immunoassay, different immobilization methods were tested and investigated with regard to their resulting target signal strength. The dependency of the target signal on the distance to the gold surface was investigated utilizing polyelectrolyte bilayers of different thickness. It could be experimentally demonstrated how much the LSPR-shift triggered by a binding event on the gold nanoparticles decreases with increasing distance to the gold surface. Thus, the sensitivity of an LSPR assay is influenced by the choice of immobilization chemistry.

Tailoring noble metal nanoparticle designs to enable sensitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) with gold nanoparticles (AuNPs) as signal reporters is a popular point-of-care diagnostic technique. However, given the weak absorbance of traditional 20-40 nm spherical AuNPs, their sensitivity is low, which greatly limits the wide application of AuNP-based LFIA. With the rapid advances in materials science and nanotechnology, the synthesis of noble metal nanoparticles (NMNPs) has enhanced physicochemical properties such as optical, plasmonic, catalytic, and multifunctional activity by simply engineering their physical parameters, including the size, shape, composition, and external structure. Using these engineered NMNPs as an alternative to traditional AuNPs, the sensitivity of LFIA has been significantly improved, thereby greatly expanding the working range and application scenarios of LFIA, particularly in trace analysis. Therefore, in this review, we will focus on the design of engineered NMNPs and their demonstration in improving LFIA. We highlight the strategies available for tailoring NMNP designs, the effect of NMNP engineering on their performance, and the working principle of each engineering design for enhancing LFIA. Finally, current challenges and future improvements in this field are briefly discussed.

Development of a gold-nanorod-based lateral flow immunoassay for a fast and dual-modal detection of C-reactive protein in clinical plasma samples

Fast and simple detection of C-reactive protein (CRP) is highly significant for the diagnosis and prognosis of inflammatory or infectious diseases. Lateral flow immunoassay has the advantages of rapid detection, simple operation and low cost, but it is usually limited by the quantitative ability and speed of data extraction. Herein, a gold-nanorod-based lateral flow immunoassay was developed to rapidly detect CRP by simultaneously monitoring the colorimetric and temperature signals. In this method, anti-CRP antibody-modified gold nanorods (GNRs) were designed as colorimetric and photothermal conversion probes. A mouse anti-CRP monoclonal antibody and goat anti-mouse IgG were used as test and control lines, respectively. Then, a lateral flow immunochromatographic strip was constructed by a sandwich-type method for detecting CRP by introducing antibody-modified GNRs, and this procedure needed less than 15 min. Finally, the detection signals can be directly observed by eyes and directly read using a thermal imager. The as-synthesized GNR showed high photothermal conversion efficiency (η = 39%) and strong localized surface plasmon resonance (LSPR) absorption. For CRP detection, the proposed immunochromatographic strip exhibited good specificity, high sensitivity, good linearity within the range of 50-10 000 ng mL-1 and a low limit of detection (LOD, 1.3 ng mL-1). This method was successfully applied for CRP detection in clinical plasma samples, and it correlated very well with the diagnostic kit of immunoturbidimetry (r = 0.96). The results indicated that the developed GNR-based immunochromatographic strip has immense potential for use as a rapid and cost-effective in vitro diagnostic kit.

Surface engineering strategies of gold nanomaterials and their applications in biomedicine and detection

Gold nanomaterials have potential applications in biosensors and biomedicine due to their controllable synthesis steps, high biocompatibility, low toxicity and easy surface modification. However, there are still various limitations including low water solubility and stability, which greatly affect their applications. In addition, some synthetic methods are very complicated and costly. Therefore, huge efforts have been made to improve their properties. This review mainly introduces the strategies for surface modification of gold nanomaterials, such as amines, biological small molecules and organic small molecules as well as the biological applications of these functionalized AuNPs. We aim to provide effective ideas for better functionalization of gold nanomaterials in the future.

Dual-Modal Immunosensor with Functionalized Gold Nanoparticles for Ultrasensitive Detection of Chloroacetamide Herbicides

Convenient and ultrasensitive detection of pesticides is demanded for healthcare and environmental monitoring, which can be realized with a dual-modal strategy. In this paper, based on a biotin-labeled IgG-modified gold nanoparticle (AuNP@IgG-bio) probe, a dual-modal immunosensor was proposed for detecting chloroacetamide herbicides. This platform is relied on the dephosphorylation of ascorbic acid 2-phosphate (AA2P) by alkaline phosphatase (ALP). In addition to this process, ascorbic acid (AA)-triggered deposition of silver on gold nanostars (AuNSs) and the fluorogenic reaction of dehydrogenated AA and o-phenylenediamine (OPD) occur sequentially. Thus, the dual readout of the color change of red-green-blue (RGB) and fluorescence generation in situ induced by crystal growth can be used. The limits of detection (LODs) were as low as 1.20 ng/mL of acetochlor (ATC), 0.89 ng/mL of metolachlor, 1.22 ng/mL of propisochlor, and 0.99 ng/mL of their mixture by a smartphone and 0.44 ng/mL of ATC, 1.59 ng/mL of metolachlor, 2.80 ng/mL of propisochlor, and 0.72 ng/mL of their mixture by a spectrofluorometer. The recoveries from corn were 91.4-105.1% of the colorimetric mode and 92.4-106.2% of the fluorescent mode. Due to its simple observation mode and good performance, this dual-modal immunosensor possesses considerable application prospects.

(Nano)tag-antibody conjugates in rapid tests

Antibodies (Abs) are naturally derived materials with favorable affinity, selectivity, and fast binding kinetics to the respective antigens, which enables their application as promising recognition elements in the development of various types of biosensors/bioassays, especially in rapid tests. These tests are low-cost and easy-to-use biosensing devices with broad applications including medical or veterinary diagnostics, environmental monitoring and industrial usages such as safety and quality analysis in food, providing on-site quick monitoring of various analytes, making it possible to save analysis costs and time. To reach such features, the conjugation of Abs with various nanomaterials (NMs) as tags is necessary, which range from conventional gold nanoparticles to other nanoparticles recently introduced, where magnetic, plasmonic, photoluminescent, or multi-modal properties play a critical role in the overall performance of the analytical device. In this context, to preserve the Ab affinity and provide a rapid response with long-term storage capability, the use of efficient bio-conjugation techniques is critical. Thanks to their prominent role in rapid tests, many studies have been devoted to the design and development of Abs-NMs conjugates with various chemistries including passive adsorption, covalent coupling, and affinity interactions. In this review, we present the state-of-the-art techniques allowing various Ab-NM conjugates with a special focus on the efficiency of the developed probes to be employed in in vitro rapid tests. Challenges and future perspectives on the development of Ab-conjugated nanotags in rapid diagnostic tests are highlighted along with a survey of the progress in commercially available Ab-NM conjugates.