Noble Metal Nanoparticle Biosensors: From Fundamental Studies toward Point-of-Care Diagnostics

Fluorescent metal nanoclusters: From luminescence mechanism to applications in enzyme activity assays

Metal nanoclusters (MNCs) have outstanding fluorescence property and biocompatibility, which show widespread applications in biological analysis. Particularly, evaluation of enzyme activity with the fluorescent MNCs has been developed rapidly within the past several years. In this review, we first introduced the fluorescent mechanism of mono- and bi-metallic nanoclusters, respectively, whose interesting luminescence properties are mainly resulted from electron transfer between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Meanwhile, the charge migration within the structure occurs through ligand-metal charge transfer (LMCT) or ligand-metal-metal charge transfer (LMMCT). On such foundation, diverse enzyme activities were rigorously evaluated, including three transferases and nine hydrolases, in turn harvesting rapid research progresses within past 5 years. Finally, we summarized the design strategies for evaluating enzyme activity with the MNCs, presented the major issues and challenges remained in the relevant research, coupled by showing some improvement measures. This review will attract researchers dedicated to the studies of the MNCs and provide some constructive insights for their further applications in enzyme analysis.

Biosensors for Public Health and Environmental Monitoring: The Case for Sustainable Biosensing

Climate change is a profound crisis that affects every aspect of life, including public health. Changes in environmental conditions can promote the spread of pathogens and the development of new mutants and strains. Early detection is essential in managing and controlling this spread and improving overall health outcomes. This perspective article introduces basic biosensing concepts and various biosensors, including electrochemical, optical, mass-based, nano biosensors, and single-molecule biosensors, as important sustainability and public health preventive tools. The discussion also includes how the sustainability of a biosensor is crucial to minimizing environmental impacts and ensuring the long-term availability of vital technologies and resources for healthcare, environmental monitoring, and beyond. One promising avenue for pathogen screening could be the electrical detection of biomolecules at the single-molecule level, and some recent developments based on single-molecule bioelectronics using the Scanning Tunneling Microscopy-assisted break junctions (STM-BJ) technique are shown here. Using this technique, biomolecules can be detected with high sensitivity, eliminating the need for amplification and cell culture steps, thereby enhancing speed and efficiency. Furthermore, the STM-BJ technique demonstrates exceptional specificity, accurately detects single-base mismatches, and exhibits a detection limit essentially at the level of individual biomolecules. Finally, a case is made here for sustainable biosensors, how they can help, the paradigm shift needed to achieve them, and some potential applications.

Antitoxin nanoparticles: design considerations, functional mechanisms, and applications in toxin neutralization

The application of nanotechnology has significantly advanced the development of novel platforms that enhance disease treatment and diagnosis. A key innovation in this field is the creation of antitoxin nanoparticles (ATNs), designed to address toxin exposure. These precision-engineered nanosystems have unique physicochemical properties and selective binding capabilities, allowing them to effectively capture and neutralize toxins from various biological, chemical, and environmental sources. In this review, we thoroughly examine their therapeutic and diagnostic potential for managing toxin-related challenges. We also explore recent advancements and offer critical insights into the design and clinical implementation of ATNs.

Weak Value Amplification-Based Biochip for Highly Sensitive Detection and Identification of Breast Cancer Exosomes

Exosomes constitute an emerging biomarker for cancer diagnosis because they carry multiple proteins that reflect the origins of the parent cell. The highly sensitive detection of exosomes is a crucial prerequisite for the diagnosis of cancer. In this study, we report an exosome detection system based on quantum weak value amplification (WVA). The WVA detection system consists of a reflection detection light path and a Zr-ionized biochip. Zr-ionized biochips effectively capture exosomes through the specific interaction between zirconium dioxide and the phosphate groups on the lipid bilayer of exosomes. Aptamer-modified gold nanoparticles (Au NPs) are then used to specifically recognize proteins on exosomes to enhance the detection signal. The sensitivity and resolution of the detection system are 2944.07 nm/RIU and 1.22 × 10-5 RIU, respectively. The concentration of exosomes can be directly quantified by the WVA system, ranging from 105-107 particles/mL with the detection limit of 3 × 104 particles/mL. The use of Au NPs-EpCAM for the specific enhancement of breast cancer MDA-MB-231 exosomes is demonstrated. The results indicate that the WVA detection system can be a promising candidate for the detection of exosomes as tumor markers.

Naked-eye rapid recognition of tyrosine enantiomers using silver triangular nanoplates as colorimetric probe

Recognizing and quantifying enantiomers of chiral molecule is of great importance in chemical, biological and pharmaceutical fields. Herein, we presented one simple-yet-efficient method of sensing tyrosine (Tyr) enantiomers. In this sensing, silver triangular nanoplates (AgTNPs) were used as colorimetric probes. L-Tyr quickly induced the color of AgTNPs solution to change from dark blue to light gray, whereas D-Tyr induced no change of the AgTNPs solution color. The obvious color change enables the naked eye to recognize Tyr enantiomer. The visual method was used to detect the enantiometric excess value of L-Tyr in the whole range (-100 % ∼ 100 %). This chiral sensing can be finished within 5 min using one simple ultraviolet-visible spectrometer or naked eye. Furthermore, the mechanism of this chiral sensing was explored. It was confirmed that this chiral sensing was based on AgTNPs' intrinsic chirality. This chiral sensing is rapid, simple, and low-cost, and has great potential for chiral determination of Tyr.

Enhanced "Electronic Tongue" for Dental Bacterial Discrimination and Elimination Based on a DNA-Encoded Nanozyme Sensor Array

Bacterial infections are the second leading cause of death around the world, especially those caused by delayed treatment and misdiagnosis. Therefore, rapid discrimination and effective elimination of multiple bacteria are of great importance for improving the survival rate in clinic. Herein, a novel colorimetric sensor array for bacterial discrimination and elimination is constructed using programmable DNA-encoded iron oxide nanoparticles (IONPs) as sensing elements. Utilizing differential interactions of bacteria on DNA-encoded IONPs, 11 kinds of dental bacteria and 6 kinds of proteins have been successfully identified by linear discriminant analysis (LDA). Moreover, the developed sensing system also performs well in the quantitative determination of individual bacteria and identification of bacterial mixtures. More importantly, the practicability of this sensing strategy is further verified by precise differentiation of blind and artificial saliva samples. Furthermore, the sensor array is used for efficiently killing multiple bacteria, demonstrating great potential in clinical prophylaxis and therapy.

Nanotechnology's frontier in combatting infectious and inflammatory diseases: prevention and treatment

Inflammation-associated diseases encompass a range of infectious diseases and non-infectious inflammatory diseases, which continuously pose one of the most serious threats to human health, attributed to factors such as the emergence of new pathogens, increasing drug resistance, changes in living environments and lifestyles, and the aging population. Despite rapid advancements in mechanistic research and drug development for these diseases, current treatments often have limited efficacy and notable side effects, necessitating the development of more effective and targeted anti-inflammatory therapies. In recent years, the rapid development of nanotechnology has provided crucial technological support for the prevention, treatment, and detection of inflammation-associated diseases. Various types of nanoparticles (NPs) play significant roles, serving as vaccine vehicles to enhance immunogenicity and as drug carriers to improve targeting and bioavailability. NPs can also directly combat pathogens and inflammation. In addition, nanotechnology has facilitated the development of biosensors for pathogen detection and imaging techniques for inflammatory diseases. This review categorizes and characterizes different types of NPs, summarizes their applications in the prevention, treatment, and detection of infectious and inflammatory diseases. It also discusses the challenges associated with clinical translation in this field and explores the latest developments and prospects. In conclusion, nanotechnology opens up new possibilities for the comprehensive management of infectious and inflammatory diseases.

Enhancement of telomerase extension via quadruple nucleic acid recycling to develop a novel colorimetric biosensing method for kanamycin assay

BACKGROUND

Colorimetric biosensors have important value for antibiotic residue testing. However, many previous methods were constructed based on the optical density change of certain unstable single-colored products with poor discrimination for visual measurements. Moreover, their low extinction coefficients usually result in low sensitivity of biosensors. In addition, many conventional signal amplification strategies often involve sophisticated nanomaterial preparation, inconvenient multi-step assay manipulation and limited signal amplification ability. Therefore, the development of new colorimetric biosensing strategies with excellent visual discrimination, high sensitivity and convenient manipulation is highly desirable.

RESULTS

We designed a target recycling accelerated cascade DNA walking amplification mechanism to trigger a telomerase extension-related enzymatic reaction, and developed a novel colorimetric biosensing strategy for kanamycin (Kana) assay. The target recycling was induced by an exonuclease III-assisted aptamer recognition reaction, which could also trigger the successive DNA walking at the streptavidin (SA)- and magnetic bead (MB)-based tracks. This not only caused the quantitative exposure of the telomeric substrate primers on MB surfaces but also released another strand to accelerate the SA-based DNA walking. By using the telomerase extension product to link numerous alkaline phosphatases and induce the plasmonic property change of gold nanobipyramids (Au NBPs), a colorimetric signal output strategy was constructed. This method could be applied for the high-resolution visual screening of Kana, and it also showed a very low detection limit of 17.6 fg mL-1 for assaying Kana over a wide, five-order-magnitude linear range.

SIGNIFICANCE

The quadruple nucleic acid recycling-enhanced telomerase extension resulted in the ultrahigh sensitivity of the method and also excluded the sophisticated manipulations involved in conventional biosensing strategies. The multiple enzyme catalysis-induced plasmonic property change of Au NBPs realized the stable and multicolor visual signal transduction. Together with its low cost, simple operation, high selectivity, excellent repeatability, and reliable performances, this method exhibits great potential for use in practical applications.

Employing Pd nanoparticles decorated on halloysite nanotube/carbon composite for electrochemical aptasensing of HER2 in breast cancer patients

An effective biosensing platform is described based on halloysite nanotube/carbon composite decorated with Pd nanoparticles (HNT/C@Pd NPs). A novel electrochemical aptasensor was designed using the proposed nano-platform to determine human epidermal growth factor receptor 2 (HER2), a breast cancer biomarker. Inherently, aptasensing interfaces provide high sensitivity and selectivity for tumor markers owing to the high specific surface area of HNT/C and good conductivity stems from deposition of Pd NPs into HNT/C composite. With a correlation coefficient of 0.996, the electrochemical aptasensor demonstrated a wide linear range from 0.03 ng/mL to 9 ng/mL. The limit of detection (LOD) of the established assay was 8 pg/mL based on S/N = 3 method. Further, the designed biosensor demonstrated acceptable selectivity, good reproducibility, and high stability. The applicability of the impedimetric sensor in human serum samples was also examined and compared to enzyme-linked immunosorbent assay (ELISA) assay (p-value >0.05). Based on the results, it was found that the proposed methodology can be used in quantification of breast cancer markers for early diagnosis and treatment.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Magnetoplasmonic gold nanorods for the sensitive and label-free detection of glutathione

This work exploits the magneto-optical activity of gold nanorods for the detection of sub-micromolar concentrations of glutathione using magnetic circular dichroism spectroscopy. Modulations of the magnetoplasmonic response of nanorods serve as the basis of the sensing methodology, whereby the presence of glutathione induces the end-to-end assembly of nanorods. In particular, the nanorod self-assembly enables a localized electric field in the nanocavities with adsorbed thiol molecules, whose field strength is amplified by the external magnetic field as confirmed by finite-element modeling, enabling their high-sensitivity detection. Our simple magnetoplasmonic sensor for glutathione requires no specific chemical tags and exhibits an impressive limit of detection of 97 nM.

Advancements in Biosensors Based on the Assembles of Small Organic Molecules and Peptides

Over the past few decades, molecular self-assembly has witnessed tremendous progress in a variety of biosensing and biomedical applications. In particular, self-assembled nanostructures of small organic molecules and peptides with intriguing characteristics (e.g., structure tailoring, facile processability, and excellent biocompatibility) have shown outstanding potential in the development of various biosensors. In this review, we introduced the unique properties of self-assembled nanostructures with small organic molecules and peptides for biosensing applications. We first discussed the applications of such nanostructures in electrochemical biosensors as electrode supports for enzymes and cells and as signal labels with a large number of electroactive units for signal amplification. Secondly, the utilization of fluorescent nanomaterials by self-assembled dyes or peptides was introduced. Thereinto, typical examples based on target-responsive aggregation-induced emission and decomposition-induced fluorescent enhancement were discussed. Finally, the applications of self-assembled nanomaterials in the colorimetric assays were summarized. We also briefly addressed the challenges and future prospects of biosensors based on self-assembled nanostructures.

Electrochemical Sensor Based on Laser-Induced Graphene for Carbendazim Detection in Water

Carbendazim (CBZ) abuse can lead to pesticide residues, which may threaten the environment and human health. In this paper, a portable three-electrode sensor based on laser-induced graphene (LIG) was proposed for the electrochemical detection of CBZ. Compared with the traditional preparation method of graphene, LIG is prepared by exposing the polyimide film to a laser, which is easily produced and patterned. To enhance the sensitivity, platinum nanoparticles (PtNPs) were electrodeposited on the surface of LIG. Under optimal conditions, our prepared sensor (LIG/Pt) has a good linear relationship with CBZ concentration in the range of 1-40 μM, with a low detection limit of 0.67 μM. Further, the sensor shows good recovery rates for the detection of CBZ in wastewater, which provides a fast and reliable method for real-time analysis of CBZ residues in water samples.

Synthesis and luminescence monitoring of iridium(III) complex-functionalized gold nanoparticles and their application for determination of gold(III) ions

A new method is presented for the one-step synthesis and real-time monitoring of iridium(III) complex-functionalized AuNPs from the precursor gold(III) chloride (AuCl₃). The functionalized AuNPs with an average size of 8 - 20 nm were obtained by the reduction of Au³⁺ ions by the alkyne group of iridium(III) complexes, which was accompanied by the anchoring iridium(III) complexes on the surface of the nanoparticles. Meanwhile, the luminescence of the iridium(III) complexes was effectively quenched due to distance-dependent fluorescence quenching by AuNPs, thereby enabling luminescence monitoring of the formation process of the functionalized AuNPs and obtaining scattering information and spectral information in real time. Moreover, this method was applied to the determination of Au³⁺ ions in buffer with a limit of detection of 0.38 μM at 700 nm in luminescence mode, while the detection limit for absorbance was 10.04 μM. Importantly, the multimodal detection strategy alleviates interference from other metal ions. Furthermore, the iridium(III) alkyne complexes were capable of imaging mitochondrial Au³⁺ ions in living cells. Taken together, this work opens a new avenue for convenient synthesis and monitoring formation of functionalized AuNPs, and also provides a tool for selective determination of Au³⁺ ions in solution and in cellulo.

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions-whether or not, as a result of a dynamically applied stimulus-and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components.

Color Transferability from Solution to Solid Using Silica Coated Silver Nanoparticles

The interpretation of color change in sensors and tests can be linked to incorrect conclusions if the intrinsic color changes are not accounted for. In this work, we study the intrinsic color change associated with the process of embedding nanoparticles in a polymer to create nanocomposite films. We present a safer, faster method to coat silver nanoparticles with silica and employ a seven-factor Plackett-Burman design to identify critical factors in the synthesis. Silver nanodisks with increasing thicknesses of the silica shell showed a decreasing sensitivity of their localized surface plasmon resonance (LSPR) toward changes in the refractive index surrounding the nanoparticle. A color shift of up to 72 nm was observed when bare nanoparticles were embedded in poly(vinyl alcohol), but no color change was perceived when nanoparticles were coated with a 25-nm-thick silica shell. Understanding the origin of color changes intrinsic to the preparation of polymeric nanocomposites aids in the design and correct use of plasmonic sensors.

Plasmonic/magnetic nanoarchitectures: From controllable design to biosensing and bioelectronic interfaces

Controllable design of the nanocrystal-assembled plasmonic/magnetic nanoarchitectures (P/MNAs) inspires abundant methodologies to enhance light-matter interactions and control magnetic-induced effects by means of fine-tuning the morphology and ordered packing of noble metallic or magnetic building blocks. The burgeoning development of multifunctional nanoarchitectures has opened up broad range of interdisciplinary applications including biosensing, in vitro diagnostic devices, point-of-care (POC) platforms, and soft bioelectronics. By taking advantage of their customizability and efficient conjugation with capping biomolecules, various nanoarchitectures have been integrated into high-performance biosensors with remarkable sensitivity and versatility, enabling key features that combined multiplexed detection, ease-of-use and miniaturization. In this review, we provide an overview of the representative developments of nanoarchitectures that being built by plasmonic and magnetic nanoparticles over recent decades. The design principles and key mechanisms for signal amplification and quantitative sensitivity have been explored. We highlight the structure-function programmability and prospects of addressing the main limitations for conventional biosensing strategies in terms of accurate selectivity, sensitivity, throughput, and optoelectronic integration. State-of-the-art strategies to achieve affordable and field-deployable POC devices for early multiplexed detection of infectious diseases such as COVID-19 has been covered in this review. Finally, we discuss the urgent yet challenging issues in nanoarchitectures design and related biosensing application, such as large-scale fabrication and integration with portable devices, and provide perspectives and suggestions on developing smart biosensors that connecting the materials science and biomedical engineering for personal health monitoring.

Enzyme-assisted metal nanoparticles etching based plasmonic ELISA: Progress and insights

The unique size and shape tunable localized surface plasmon resonance (LSPR) properties of the noble metal nanoparticle have been extensively exploited to realize a variety of enzyme-based optical biosensors. Although approaches like metal film deposition, nanoparticle aggregation, and synthesis & growth of metal nanoparticles are quite useful, metal nanoparticle etching-based biosensors offer greater sensitivity, selectivity, and stability against various environmental factors which makes this strategy easy to use for field applications. This review discusses the current state-of-art of plasmonic nanoparticle etching-based enzyme-linked immunosorbent assay (ELISA) realized for visual detection of various analytes. The naked eye detection, i.e. without any optical readout device, is the additional advantage of this sensing approach that reduces the analysis cost significantly making it feasible under resource-constrained settings. This review paper provides deeper insights into biocatalytic etching mechanisms of various plasmonic nanoparticles resulting in vivid color change as a function of analyte concentration. Although nanoparticle etching-based ELISA has huge potential, steps need to be taken to realize a point-of-care (POC) nanodiagnostic before its translation to a commercial technique or product that can be achieved in near future by integrating it with microfluidics technology and other technological avenues.

Controlled Synthesis of Platinum and Silver Nanoparticles Using Multivalent Ligands

Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step process. PtNPs and AgNPs were prepared in the presence of amine ligands using platinum (II) acetylacetonate and silver (I) acetylacetonate, respectively. The effects of ligands and temperature on the formation of PtNPs were studied using a transmission electron microscope (TEM). For the characterization of AgNPs, additionally, ultraviolet-visible (UV-Vis) absorption was employed. The TEM measurements revealed that PtNPs prepared at different temperatures (160–200 °C, in a stepwise process) are monodispersed and of spherical shape regardless of the ligand multivalency or reaction temperature. In the preparation of PtNPs by the one-step process, ligands affect the shape of the PtNPs, which can be explained by the affinity of the ligands. The TEM and UV-Vis absorption studies on the formation of AgNPs with mono-, di-, and trivalent ligands showed narrower size distributions, while increasing the temperature from 80 °C to 120 °C and with a trivalent ligand in a one-step process.