An Individual Nanocube-Based Plasmonic Biosensor for Real-Time Monitoring the Structural Switch of the Telomeric G-Quadruplex

Plasmonic nanosensors for point-of-care biomarker detection

Advancement of materials along with their fascinating properties play increasingly important role in facilitating the rapid progress in medicine. An excellent example is the recent development of biosensors based on nanomaterials that induce surface plasmon effect for screening biomarkers of various diseases ranging from cancer to Covid-19. The recent global pandemic re-confirmed the trend of real-time diagnosis in public health to be in point-of-care (POC) settings that can screen interested biomarkers at home, or literally anywhere else, at any time. Plasmonic biosensors, thanks to its versatile designs and extraordinary sensitivities, can be scaled into small and portable devices for POC diagnostic tools. In the meantime, efforts are being made to speed up, simplify and lower the cost of the signal readout process including converting the conventional heavy laboratory instruments into lightweight handheld devices. This article reviews the recent progress on the design of plasmonic nanomaterial-based biosensors for biomarker detection with a perspective of POC applications. After briefly introducing the plasmonic detection working mechanisms and devices, the selected highlights in the field focusing on the technology's design including nanomaterials development, structure assembly, and target applications are presented and analyzed. In parallel, discussions on the sensor's current or potential applicability in POC diagnosis are provided. Finally, challenges and opportunities in plasmonic biosensor for biomarker detection, such as the current Covid-19 pandemic and its testing using plasmonic biosensor and incorporation of machine learning algorithms are discussed.

Au nanoparticles deposited on ultrathin two-dimensional covalent organic framework nanosheets for in vitro and intracellular sensing

A novel composite nanomaterial is prepared by growing small Au nanoparticles on two-dimensional covalent organic framework nanosheets (Au NPs/COF NSs). The synthesized hybrid nanosheets are used as a new platform for multiplexed detection of hepatitis A virus DNA (HAV) and hepatitis B virus DNA (HBV). Additionally, this sensing platform based on Au NPs/COF NSs can be used as a candidate for monitoring the distribution of potassium ions (K⁺) and the intracellular K⁺ level in living cells. Accordingly, the sensing systems based on hybrid Au NPs/COF NSs have shown great potential for the investigation of biomolecules and related biological applications.

Surface enhanced Raman scattering substrate for the detection of explosives: Construction strategy and dimensional effect

Surface-enhanced Raman spectroscopy (SERS) technology has been reported to be able to quickly and non-destructively identify target analytes. SERS substrate with high sensitivity and selectivity gave SERS technology a broad application prospect. This contribution aims to provide a detailed and systematic review of the current state of research on SERS-based explosive sensors, with particular attention to current research advances. This review mainly focuses on the strategies for improving SERS performance and the SERS substrates with different dimensions including zero-dimensional (0D) nanocolloids, one-dimensional (1D) nanowires and nanorods, two-dimensional (2D) arrays, and three-dimensional (3D) networks. The effects of elemental composition, the shape and size of metal nanoparticles, hot-spot structure and surface modification on the performance of explosive detection are also reviewed. In addition, the future development tendency and application of SERS-based explosive sensors are prospected.

Development and Validation of a Specific RP-HPLC Method for Simultaneous Estimation of Anti-retroviral Drugs: Application to Nanoparticulate Formulation System

Objective:

A simple, accurate and economical reverse phase- high performance liquid chromatographic method has been developed for the simultaneous quantitative estimation of two anti-retro viral drugs, Etravirine and Elvitegravir in nanoparticulate formulations for the first time. This method is a novel analytical technique for the detection of the both the drugs concurrently, as there is no method available for their simultaneous quantification, to the best of our knowledge.

Methods:

Optimization and validation of the chromatographic conditions were completed according to the standard ICH guidelines. The separation was done on a C18 column (250 mm x 4.6mm, 5μm) using methanol and phosphate buffer of pH (5.6) as the mobile phase in the ratio 78:22 v/v at a flow rate of 1ml/min for a short run time of 13 min. The detection wavelength was 285nm and the column temperature was maintained at 32oC.

Results:

The developed method was linear over 10 to 160 μg/ml with a regression coefficient of 0.999 for each. The LOD values were 4.83 and 9.25 µg/ml while LOQ values were 14.63 and 28.01 µg/ml for etravirine and elvitegravir respectively. The recovery values obtained by etravirine and elvitegravir were between 97.6% and 100.8%.

Conclusion:

The method was specific, precise, fast and accurate with good inter and intra day precision. The method was also effectively employed for the characterization and simultaneous quantification of both drugs in nanoparticulate formulation.

Gold Nanomaterials for Imaging-Guided Near-Infrared in vivo Cancer Therapy

In recent years, tremendous efforts have been devoted into the fields of valuable diagnosis and anticancer treatment, such as real-time imaging, photothermal, and photodynamic therapy, and drug delivery. As promising nanocarriers, gold nanomaterials have attracted widespread attention during the last two decades for cancer diagnosis and therapy due to their prominent properties. With the development of nanoscience and nanotechnology, the fascinating bio-applications of functionalized gold nanomaterials have been gradually developed from in vitro to in vivo. This mini-review emphasizes some recent advances of photothermal imaging (PTI), surface-enhanced Raman scattering (SERS) imaging, and photoacoustic imaging (PAI)-guided based on gold nanomaterials in vivo therapy in near infrared region (>800 nm). We focus on the fundamental strategies, characteristics of bio-imaging modalities involving the advantages of multiples imaging modalities for cancer treatment, and then highlight a few examples of each techniques. Finally, we discuss the perspectives and challenges in gold nanomaterial-based cancer therapy.

Dark-field spectroscopy: development, applications and perspectives in single nanoparticle catalysis

Dark-field microscopy (DFM) is an effective method to detect the scattering signal from single nanoparticles. This technique could break through the 200 nm limit resolution of ordinary optical microscopes. It even can observe the submicron particles of 20-200 nm. Moreover, from 2000, DFM was coupled with a spectrometer to measure the scattering spectra of single silver nanoparticles. Then, dark-field spectroscopy becomes a very important plasmon spectroscopy technique for single nanoparticles. Usually, plasmonic nanoparticles are the major research target, because they have unique optical properties due to their localized surface plasmon resonance (LSPR), which can be influenced by many factors, such as composition, size, morphology, the refractive index of the surrounding medium etc. When surface chemical reactions occur on a single nanoparticle, it could induce the variation of these factors. Then, the structure-activity relationship for these nanoparticle catalysts can be studied at a single nanoparticle level and in real time. This review mainly summarized the development of dark-field spectroscopy, spectrometers, light sources, and other accessories, which greatly improved the imaging capabilities of dark-field spectroscopy. Meanwhile, the applications of dark-field spectroscopy in single-particle catalysis such as chemocatalysis, photocatalysis, electrocatalysis and biocatalysis are also reviewed.

Revealing Lectin-Sugar Interactions with a Single Au@Ag Nanocube

An individual nanoparticle-based plasmonic nanotechnology was used for real-time monitoring of lectin-sugar interactions, which could be designed as novel plasmonic nanobiosensors for the detection of trace concanavalin A (ConA) with high sensitivity and selectivity. The localized surface plasmon resonance (LSPR) spectra of Au@Ag nanocubes (NCs) are linearly shifted to a long wavelength with an increasing concentration of ConA. In fact, each Au@Ag NC can act as a nanobiosensor for the quantified detection of trace ConA, which enables the miniaturization of the biosensor system to nanoscale. Furthermore, the results demonstrated the perfect biosensing ability with the dual channel of dark-field microscopy images and LSPR spectra. We expect that this nanobiosensor system can provide an alternative important method for monitoring the specific binding of lectin-sugar at a single nanoparticle surface.

DNA-Functionalized Plasmonic Nanomaterials for Optical Biosensing

Plasmonic nanomaterials, especially Au and Ag nanomaterials, have shown attractive physicochemical properties, such as easy functionalization and tunable optical bands. The development of this active subfield paves the way to the fascinating biosensing platforms. In recent years, plasmonic nanomaterials-based sensors have been extensively investigated because they are useful for genetic diseases, biological processes, devices, and cell imaging. In this account, a brief introduction of the development of optical biosensors based on DNA-functionalized plasmonic nanomaterials is presented. Then the common strategies for the application of the optical sensors are summarized, including colorimetry, fluorescence, localized surface plasmon resonance, and surface-enhanced resonance scattering detection. The focus is on the fundamental aspect of detection methods, and then a few examples of each method are highlighted. Finally, the opportunities and challenges for the plasmonic nanomaterials-based biosensing are discussed with the development of modern technologies.

Sequence Dynamics of Pre-mRNA G-Quadruplexes in Plants

Intramolecular G-quadruplexes (G4s) are secondary structures that may form within G-rich stretches of nucleic acids. Although their presence has been associated with genomic instability and mutagenicity, recent reports suggest their involvement in regulation of diverse cellular events, including transcription and translation. The majority of data regarding G4s stems from mammalian and yeast studies, leaving the plant G4s almost unexplored. Using the publicly available Arabidopsis thaliana and Oryza sativa WGS data, we examined the single nucleotide variability of sequences predicted to form G4s (pG4s) structures. We focused our analysis on protein coding transcripts and compared the results to well-characterized Homo sapiens data. We demonstrate that the overall high variability of pG4s is not uniform and differs between gene structural elements. Specifically, plant AUG-containing pG4s, located within 5'UTR/CDS junctions, are abundant and appear not to be affected by a higher frequency of sequence change, indicating their functional relevance. Furthermore, we show that substitutions lowering the probability of G4s' formation are preferred over neutral or stabilizing modifications.

Plasmonic Heterodimers with Binding Site-Dependent Hot Spot for Surface-Enhanced Raman Scattering

A novel plasmonic heterodimer nanostructure with a controllable self-assembled hot spot is fabricated by the conjugation of individual Au@Ag core-shell nanocubes (Au@Ag NCs) and varisized gold nanospheres (GNSs) via the biotin-streptavidin interaction from the ensemble to the single-assembly level. Due to their featured configurations, three types of heterogeneous nanostructures referred to as Vertice, Vicinity, and Middle are proposed and a single hot spot forms between the nanocube and nanosphere, which exhibits distinct diversity in surface plasmon resonance effect. Herein, the calculated surface-enhanced Raman scattering enhancement factors of the three types of heterodimers show a narrow distribution and can be tuned in orders of magnitude by controlling the size of GNSs onto individual Au@Ag NCs. Particularly, the Vertice heterodimer with unique configuration can provide extraordinary enhancement of the electric field for the single hot spot region due to the collaborative interaction of lightning rod effect and interparticle plasmon coupling effect. This established relationship between the architecture and the corresponding optical properties of the heterodimers provides the basis for creating controllable platforms which can be exploited in the applications of plasmonic devices, electronics, and biodetection.

Nanoplasmonic sensors for biointerfacial science

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

Imaging the chemical activity of single nanoparticles with optical microscopy

Chemical activity of single nanoparticles can be imaged and determined by monitoring the optical signal of each individual during chemical reactions with advanced optical microscopes. It allows for clarifying the functional heterogeneity among individuals, and for uncovering the microscopic reaction mechanisms and kinetics that could otherwise be averaged out in ensemble measurements.

Individual Au-Nanocube Based Plasmonic Nanoprobe for Cancer Relevant MicroRNA Biomarker Detection

MicroRNA205 (miR-205), as a significant tumor biomarker, is of vital importance for diagnosis of lung cancer and its overexpression patterns have been extensively studied. Here, we report a novel and label-free nanoprobe with high sensitivity and selectivity for miRNA biomarker detection using localized surface plasmon resonance (LSPR) technology on a single DNA modified gold nanocube (AuNC). This method allowed real-time monitoring of the subtle LSPR scattering peak position's change which was aroused by the variation of dielectric constant in the hybridization process of target miRNA with ssDNA modified on the surface of AuNCs. Notably, the limit of detection of the AuNC-ssDNA probe is up to 5 pM in serum sample, and these results showed that the square structure has more superior sensitivity for design and development of nanoprobe for trace lung cancer relevant miRNAs detection. The better sensing ability and stability of LSPR probe on a AuNC provide potential application to developing a high flux biochip in the future.

In Situ Detection and Imaging of Telomerase Activity in Cancer Cell Lines via Disassembly of Plasmonic Core-Satellites Nanostructured Probe

The label-free localized surface plasmon resonance (LSPR) detection technique has been identified as a powerful means for in situ investigation of biological processes and localized chemical reactions at single particle level with high spatial and temporal resolution. Herein, a core-satellites assembled nanostructure of Au₅₀@Au₁₃ was designed for in situ detection and intracellular imaging of telomerase activity by combining plasmonic resonance Rayleigh scattering spectroscopy with dark-field microscope (DFM). The Au₅₀@Au₁₃ was fabricated by using 50 nm gold nanoparticles (Au₅₀) as core and 13 nm gold nanoparticles (Au₁₃) as satellites, both of them were functionalized with single chain DNA and gathered proximity through the highly specific DNA hybridization with a nicked hairpin DNA (O1) containing a telomerase substrate (TS) primer as linker. In the presence of telomerase, the telomeric repeated sequence of (TTAGGG)_n extended at the 3'-end of O1 would hybridized with its complementary sequences at 5'-ends. This led the telomerase extension product of O1 be folded to form a rigid hairpin structure. As a result, the Au₅₀@Au₁₃ was disassembled with the releasing of O1 and Au₁₃-S from Au₅₀-L, which dramatically decreased the plasmon coupling effect. The remarkable LSPR spectral shift was observed accompanied by a detectable color change from orange to green with the increase of telomerase activity at single particle level with a detection limit of 1.3 × 10^-13 IU. The ability of Au₅₀@Au₁₃ for in situ imaging intracellular telomerase activity, distinguishing cancer cells from normal cells, in situ monitoring the variation of cellular telomerase activity after treated with drugs were also demonstrated.

Cell-impedance-based label-free technology for the identification of new drugs

INTRODUCTION

Drug discovery has progressed from relatively simple binding or activity screening assays to high-throughput screening of sophisticated compound libraries with emphasis on miniaturization and automation. The development of functional assays has enhanced the success rate in discovering novel drug molecules. Many technologies, originally based on radioactive labeling, have sequentially been replaced by methods based on fluorescence labeling. Recently, the focus has switched to label-free technologies in cell-based screening assays. Areas covered: Label-free, cell-impedance-based methods comprise of different technologies including surface plasmon resonance, mass spectrometry and biosensors applied for screening of anticancer drugs, G protein-coupled receptors, receptor tyrosine kinase and virus inhibitors, drug and nanoparticle cytotoxicity. Many of the developed methods have been used for high-throughput screening in cell lines. Cell viability and morphological damage prediction have been monitored in three-dimensional spheroid human HT-29 carcinoma cells and whole Schistosomula larvae. Expert opinion: Progress in label-free, cell-impedance-based technologies has facilitated drug screening and may enhance the discovery of potential novel drug molecules through, and improve target molecule identification in, alternative signal pathways. The variety of technologies to measure cellular responses through label-free cell-impedance based approaches all support future drug development and should provide excellent assets for finding better medicines.

Synthesis of hydrophilic and conductive molecularly imprinted polyaniline particles for the sensitive and selective protein detection

In this work, a novel kind of water-dispersible molecular imprinted conductive polyaniline particles was prepared through a facile and efficient macromolecular co-assembly of polyaniline with amphiphilic copolymer, and applied as the molecular recognition element to construct protein electrochemical sensor. In our strategy, an amphiphilic copolymer P(AMPS-co-St) was first synthesized using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and styrene (St) as monomer, which could co-assemble with PANI in aqueous solution to generate PANI particles driven by the electrostatic interaction. During this process, ovalbumin (OVA) as template protein was added and trapped into the PANI NPs particles owing to their interactions, resulting in the formation of molecular imprinted polyaniline (MIP-PANI) particles. When utilizing the MIP-PANI particles as recognition element, the resultant imprinted PANI sensor not only exhibited good selectivity toward template protein (the imprinting factor α is 5.31), but also a wide linear range over OVA concentration from 10^-11 to 10^-6mgmL^-1 with a significantly lower detection limit of 10^-12mgmL^-1, which outperformed most of reported OVA detecting methods. In addition, an ultrafast response time of less than 3min has also been demonstrated. The superior performance is ascribed to the water compatibility, large specific surface area of PANI particles and the electrical conductivity of PANI which provides a direct path for the conduction of electrons from the imprinting sites to the electrode surface. The outstanding sensing performance combined with its facile, quick, green preparation procedure as well as low production cost makes the MIP-PANI particles attractive in specific protein recognition and sensing.

The Effect of Adenine Repeats on G-quadruplex/hemin Peroxidase Mimicking DNAzyme Activity

The catalytic activity of G-quadruplex/hemin is much lower than that of proteinous enzymes, so it is very important to increase its activity. Very recently, flanking sequences, which can be regarded as an external part of G-quadruplexes, were found to enhance the activity of G-quadruplex/hemin DNAzyme. However, little is known about the effect of internal parts, such as loop sequences and linkers, on the activity. In the present study, adenine repeats were incorporated into several designed G-quadruplex structures either in the loops, bulges, or linkers, and the constructed G-quadruplex/hemin DNAzyme exhibit about fivefold improvement in peroxidase-mimicking activity in some cases. The enhancement effect may result from the formation of compound I, protoporphyrin⋅Fe^IV =O^.+ , accelerated by dA repeats, which was demonstrated by H₂ O₂ decay kinetics and pH dependency analysis. The novel enhancement methods described here may help in the development of high-activity DNAzymes, illustrated by a dimer G-quadruplex with flanking adenine at one end, a relatively long adenine run in one loop, and another adenine run in the linker.

Narrow band resonance in the UV light region of a plasmonic nanotextured surface used as a refractive index sensor

An aperiodic plasmoic nanotextured surface with metal-dielectric-metal (MDM) multilayer nanostructure acts as a refractive index (RI) sensor in the ultra-violet light region.