Facile synthesis of gold nanohexagons on graphene templates in Raman spectroscopy for biosensing cancer and cancer stem cells

Cell membrane-targeted surface enhanced Raman scattering nanoprobes for the monitoring of hydrogen sulfide secreted from living cells

Hydrogen sulfide (H2S), an important gas signal molecule, participates in intercellular signal transmission and plays a considerable role in physiology and pathology. However, in-situ monitoring of H2S level during the processes of material transport between cells remains considerably challenging. Herein, a cell membrane-targeted surface-enhanced Raman scattering (SERS) nanoprobe was designed to quantitatively detect H2S secreted from living cells. The nanoprobes were fabricated by assembling cholesterol-functionalized DNA strands and dithiobis(phenylazide) (DTBPA) molecules on core-shell gold nanostars embedded with 4-mercaptoacetonitrile (4-MBN) (AuNPs@4-MBN@Au). Thus, three functions including cell-membrane targeted via cholesterol, internal standard calibration, and responsiveness to H2S through reduction of azide group in DTBPA molecules were integrated into the nanoprobes. In addition, the nanoprobes can quickly respond to H2S within 90 s and sensitively, selectively, and reliably detect H2S with a limit of detection as low as 37 nM due to internal standard-assisted calibration and reaction specificity. Moreover, the nanoprobes can effectively target on cell membrane and realize SERS visualization of dynamic H2S released from HeLa cells. By employing the proposed approach, an intriguing phenomenon was observed: the other two major endogenous gas transmitters, carbon monoxide (CO) and nitric oxide (NO), exhibited opposite effect on H2S production in living cells stimulated by related gas release molecules. In particular, the introduction of CO inhibited the generation of H2S in HeLa cells, while NO promoted its output. Thus, the nanoprobes can provide a robust method for investigating H2S-related extracellular metabolism and intercellular signaling transmission.

Effect of Aspect Ratio of a Gold-Nanorod-Modified Screen-Printed Carbon Electrode for Carbaryl Detection in Three Different Samples of Vegetables

In this study, three different sizes of gold nanorods (AuNRs) were synthesized using the seed-growth method by adding various volumes of AgNO3 as 400, 600, and 800 μL into the growth solution of gold nanoparticles. Three different sizes of AuNRs were then characterized using UV-vis spectroscopy, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) patterns, and atomic force microscopy (AFM) to investigate the surface morphology, topography, and aspect ratios of each synthesized AuNR. The aspect ratios from the histogram of size distributions of three AuNRs as 2.21, 2.53, and 2.85 can be calculated corresponding to the addition of AgNO3 volumes of 400, 600, and 800 μL. Moreover, each AuNR in three different aspect ratios was drop-cast onto the surface of a commercial screen-printed carbon electrode (SPCE) to obtain three different SPCE-modified AuNRs (SPCE-A400, SPCE-A600, and SPCE-A800, respectively). All SPCE-modified AuNRs were then evaluated for their electrochemical behavior using cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques and the highest electrochemical performance was shown as the order of magnitude of SPCE-A400 > SPCE-A600/SPCE-A800. The reason for the highest electrocatalytic activity of SPCE-A400 might be due to the smallest particle size and uniform distribution of AuNRs ∼ 2.2, which enhanced the charge transfer, thus providing the highest electroactive surface area (0.6685 cm2) compared to other electrodes. These results also confirm that the sensing mechanism for all SPCE-modified AuNRs is controlled by diffusion phenomena. In addition, the optimum pH was obtained as 4 for carbaryl detection for all SPCE-modified AuNRs with the highest current shown by SPCE-A400. Furthermore, SPCE-A400 has the highest fundamental parameters (surface coverage, catalytic rate constant, electron transfer rate constant, and adsorption capacity) for carbaryl detection, which were investigated using cyclic voltammetry and chronoamperometric techniques. The electroanalytical performances of all SPCE-modified AuNRs for carbaryl detection were also investigated with SPCE-A400 displaying the best performance among other electrodes in terms of its linearity (0.2-100 μM), limit of detection (LOD) ∼ 0.07 μM, and limit of quantification (LOQ) ∼ 0.2 μM. All SPCE-modified AuNRs were also subsequently evaluated for their stability, reproducibility, and selectivity in the presence of interfering species such as NaNO2, NH4NO3, Zn(CH3CO2)2, FeSO4, diazinon, and glucose and show reliable results as depicted from %RSD values less than 3%. At last, all SPCE-modified AuNRs have been employed for carbaryl detection using a standard addition technique in three different samples of vegetables (cabbage, cucumber, and Chinese cabbage) with its results (%recovery ≈ 100%) within the acceptable analytical range. In conclusion, this work demonstrates the great potential of a disposable device based on an AuNR-modified SPCE for rapid detection and high sensitivity in monitoring the concentration of carbaryl as a residual pesticide in vegetable samples.

Preparation of gold nanoparticles loaded MOF-199 for SERS detection of 5-hydroxyindole-3-acetic acid in serum

5-Hydroxyindole-3-acetic acid (5-HIAA) is regarded as a biomarker for diagnosis of carcinoid tumors, and it is of great significance to developing a precision assay for monitoring 5-HIAA levels. In this work, gold nanoparticles loading on the surface of MOF-199 (Au NPs/MOF-199) is prepared to propose a surface enhanced Raman scattering (SERS) assay for 5-HIAA. When 4-mercaptopyridine (4-MPy) is used as a SERS probe, on Au NPs/MOF-199, limit of detection (LOD) at 10-9 mol/L can be achieved. In addition, Au NPs/MOF-199 substrate with good preparation reproducibility shows long-term storage stability at 4 °C. Under optimal condition, the Au NPs/MOF-199-based SERS method is applied to determine 5-HIAA in serum. The concentration linear range is from 10-9 to 10-5 mol/L and LOD is of 6.40 × 10-11 mol/L. Much importantly, Au NPs/MOF-199 substrate exhibits specific response toward 5-HIAA against other metabolites in the serum due to the capturing selectivity from porous MOF-199. The recoveries obtained on spiked human serum samples locate in the span from 94.30% to 106.00% with RSD of 4.01-7.43%. Au NPs/MOF-199-based SERS sensing strategy is a promising avenue for on-field monitoring biomedical species for clinic diagnosis purpose.

Ti3C2Tx MXene -facilitated non-selective trapping effect: Efficient SERS detection of exosomal PD-L1

Biosensors developed through a sandwich approach have demonstrated favorable detection performance for exosomal programmed cell death 1 ligand 1 (ExoPD-L1) detection. However, the reported PD-L1 antibodies, peptides, and aptamers utilized in these biosensors typically bind to the extracellular region, with overlapping binding sites that severely constrain the fabrication of biosensors. In this study, we present a simple approach to specifically identify and analyze ExoPD-L1 through the non-selective trapping effect of Ti3C2TX (X=-O, -F, -OH) MXene on exosomes via the formation of Ti-O-P complexation, and the selective capture of peptide-functionalized Au@MPBA (4-Mercaptophenylboronic acid) @SiO2 surface enhanced Raman scattering (SERS) tags on ExoPD-L1. The biosensor delivered a both hypersensitive and reliable performance in exosome detection with a low limit of detection (20.74 particles/mL) in the linear range of 102 to 5×106 particles/mL. Furthermore, the biosensor demonstrated excellent stability and interference resistance in detecting ExoPD-L1 in clinical serum samples, enabling the easy differentiation of breast cancer patients from healthy controls. This work provides new insights into the design of biosensors for exosome detection and can serve as a replicable template for sandwich immunoassay detection for other types of sensors, including but not limited to SERS.

Biosensing Systems Based on Graphene Oxide Fluorescence Quenching Effect

Graphene oxide (GO) is a versatile material obtained by the strong oxidation of graphite. Among its peculiar properties, there is the outstanding ability to significantly alter the fluorescence of many common fluorophores and dyes. This property has been exploited in the design of novel switch-ON and switch-OFF fluorescence biosensing platforms for the detection of a plethora of biomolecules, especially pathological biomarkers and environmental contaminants. Currently, novel advanced strategies are being developed for therapeutic, diagnostic and theranostic approaches to widespread pathologies caused by viral or bacterial agents, as well as to cancer. This work illustrates an overview of the most recent applications of GO-based sensing systems relying on its fluorescence quenching effect.

Semi-wrapped gold nanoparticles for surface-enhanced Raman scattering detection

Researchers have struggled to develop highly reliable and sensitive surface-enhanced Raman scattering (SERS) substrates for detecting compounds in complicated systems. In this work, a strategy by constructing Au cores with incompletely wrapped Prussian blue (PB) for highly reliable and sensitive SERS substrate is proposed. The wrapped PB layers can provide the internal standard (IS) to calibrate the SERS signal floatation, whereas the exposed surface of Au cores offers the enhancement effect. The balance between the signal self-calibration and enhancement (hence the trade-off between SERS reliability and sensitivity) is obtained by the approximate semi-wrapping configuration of PB layers on Au cores (i.e., SW-Au@PB). The proposed SW-Au@PB nanoparticles (NPs) exhibit the similar enhancement factor as the pristine Au NPs and contribute to the ultralow RSD (8.55%) of calibrated SERS signals using R6G as probe molecules. The simultaneously realized reliability and sensitivity of SW-Au@PB NPs also enables the detection of hazardous pesticide residues such as paraquat and thiram in herbal plants, with the average detection accuracy up to 92%. Overall, this work mainly provides a controllable synthetic strategy for incompletely wrapped NPs, and most importantly, explores the potential with a proof-of-concept practical application in accurate and sensitive Raman detection of hazardous substances with varying solubility.

Repair of critical-sized bone defects in rabbit femurs using graphitic carbon nitride (g-C3N4) and graphene oxide (GO) nanomaterials

Various biomaterials have been evaluated to enhance bone formation in critical-sized bone defects; however, the ideal scaffold is still missing. The objective of this study was to investigate the in vitro and in vivo regenerative capacity of graphitic carbon nitride (g-C₃N₄) and graphene oxide (GO) nanomaterials to stimulate critical-sized bone defect regeneration. The in vitro cytotoxicity and hemocompatibility of g-C₃N₄ and GO were evaluated, and their potential to induce the in vitro osteogenesis of human fetal osteoblast (hFOB) cells was assessed using qPCR. Then, bone defect in femoral condyles was created in rabbits and left empty as control or filled with either g-C₃N₄ or GO. The osteogenesis of the different implanted scaffolds was evaluated after 4, 8, and 12 weeks of surgery using X-ray, computed tomography (CT), macro/microscopic examinations, and qPCR analysis of osteocalcin (OC) and osteopontin (OP) expressions. Both materials displayed good cell viability and hemocompatibility with enhanced collagen type-I (Col-I), OC, and OP expressions of the hFOB cells. Compared to the control group, the bone healing process in g-C₃N₄ and GO groups was promoted in vivo. Moreover, complete healing of the bone defect was observed radiologically and grossly in g-C₃N₄ implanted group. Additionally, g-C₃N₄ implanted group showed higher percentages of osteoid tissue, mature collagen, biodegradation, and expressions of OC and OP. In conclusion, our results revealed that g-C₃N₄ and GO nanomaterials could induce osteogenesis in critical-sized bone defects.

SERS-based antibiotic susceptibility testing: Towards point-of-care clinical diagnosis

Emerging antibiotic resistant bacteria constitute one of the biggest threats to public health. Surface-enhanced Raman scattering (SERS) is highly promising for detecting such bacteria and for antibiotic susceptibility testing (AST). SERS is fast, non-destructive (can probe living cells) and it is technologically flexible (readily integrated with robotics and machine learning algorithms). However, in order to integrate into efficient point-of-care (PoC) devices and to effectively replace the current culture-based methods, it needs to overcome the challenges of reliability, cost and complexity. Recently, significant progress has been made with the emergence of both new questions and new promising directions of research and technological development. This article brings together insights from several representative SERS-based AST studies and approaches oriented towards clinical PoC biosensing. It aims to serve as a reference source that can guide progress towards PoC routines for identifying antibiotic resistant pathogens. In turn, such identification would help to trace the origin of sporadic infections, in order to prevent outbreaks and to design effective medical treatment and preventive procedures.

Nano-Ag Particles Embedded in C-Matrix: Preparation, Properties and Application in Cell Metabolism

The application of nano-Ag grains as antiviral and antibacterial materials is widely known since ancient times. The problem is the toxicity of the bulk or big-size grain materials. It is known that nano-sized silver grains affect human and animal cells in some medical treatments. The aim of this study is to investigate the influence of nano-Ag grains embedded in a carbonaceous matrix on cytotoxicity, genotoxicity in fibroblasts, and mutagenicity. The nanocomposite film is composed of silver nanograins embedded in a carbonaceous matrix and it was obtained via the PVD method by deposition from two separated sources of fullerenes and silver acetate powders. This method allows for the preparation of material in the form of a film or powder, in which Ag nanograins are stabilized by a carbon network. The structure and morphology of this material were studied using SEM/EDX, XRD, and Raman spectroscopy. The toxicology studies were performed for various types of the material differing in the size of Ag nanograins. Furthermore, it was found that these properties, such as cell viability, genotoxicity, and mutagenicity, depend on Ag grain size.

Targeting Cancer Stem Cells: Therapeutic and diagnostic strategies by the virtue of nanoparticles

Cancer stem cells (CSCs) are the subpopulation of cells present within a tumor with the properties of self-renewing, differentiating, and proliferating. Owing to the presence of ATP-binding cassette drug pumps and increased expression of anti-apoptotic proteins, the conventional chemotherapeutic agents have failed to eliminate CSCs resulting in relapse and resistance of cancer. Therefore, to obtain long-lasting clinical responses and avoid the recurrence of cancer, it is crucial to develop an efficient strategy targeting CSCs by either employing a differentiation therapy or specifically delivering drugs to CSCs. Several intracellular and extracellular cancer specific biomarkers are overexpressed by CSCs and are utilized as targets for the development of new approaches in the diagnosis and treatment of CSCs. Moreover, several nanostructured particles, alone or in combination with current treatment approaches, have been used to improve the detection, imaging, and targeting of CSCs, thus addressing the limitations of cancer therapies. Targeting CSC surface markers, stemness-related signaling pathways, and tumor microenvironmental signals has improved the detection and eradication of CSCs and, therefore, tumor diagnosis and treatment. This review summarizes a variety of promising nanoparticles targeting the surface biomarkers of CSCs for the detection and eradication of tumor-initiating stem cells, used in combination with other treatment regimens.

Surface plasmon-enhanced fluorescence and surface-enhanced Raman scattering dual-readout chip constructed with silver nanowires: Label-free clinical detection of direct-bilirubin

It has been found that the direct/total bilirubin ratio (D/T-BIL) is related to the survival rate of COVID-19 pneumonia. The presence of an excessive amount of bilirubin in human blood also causes liver and neurological damage, leading to death. Therefore, upon considering the adverse impact of the presence of excessive bilirubin in human blood, it has become highly imperative to detect bilirubin in a fast and label-free manner. Herein, we designed and constructed a random-crossed-woodpile nanostructure from silver nanowires to form a 3-dimensional plasmonic hotspot-rich (3D-PHS) nanostructure and successfully used it to detect direct bilirubin (D-BIL) in human blood in a label-free manner. The 3D-PHS nanochip provides rich spatial hot spots that are simultaneously responsive to SERS and SPEF effects and consequently, successfully used to measure and characterize D-BIL with a detection limit of ∼10 nM, requiring only 10μL of human serum for rapid screening, which is the first time D-BIL has been detected in a clinically relevant range. This demonstrates a simple, label-free, pretreatment-free potential biosensing technology that can be used in health care units, and further, in the efficient detection of point-of-care testing with a portable spectrometer.

Improvement of Transfection with PepFects Using Organic and Inorganic Materials

Cell-penetrating peptides (CPPs) are a promising non-viral vector for gene and drug delivery. CPPs exhibit high cell transfection, and are biocompatible. They can be also conjugated with organic and inorganic nanomaterials, such as magnetic nanoparticles (MNPs), graphene oxide (GO), metal-organic frameworks (MOFs), and chitosan. Nanomaterials offered a high specific surface area and provided relatively straightforward methods to be modified with biomolecules including CPPs and oligonucleotides (ONs). Novel nanomaterials conjugates with CPP/ONs complexes are therefore of interest for cell transfection with high efficiency. In this chapter, we described a summary of the non-viral vectors consisting of CPPs and nanomaterials. The book chapter also included a protocol to generate hybrid biomaterials consisting of CPPs and nanoparticles (NPs) for the delivery of oligonucleotides. The conjugation of NPs with CPPs serves as an effective platform for gene therapy with high cell transfection efficiency. The protocol is simple, offers high cell transfection compared to the CPPs-ONs complexes, and can be used for further improvements using external stimuli.

Recent Advances in Engineered Noble Metal Nanomaterials as a Surface-Enhanced Raman Scattering Active Platform for Cancer Diagnostics

Recently, noble metal nanomaterials have been extensively studied in the fields of biosensing, environmental catalysis, and cancer diagnosis and treatment, due to their excellent electrical conductivity, high surface area, and individual physical and optical properties. Early research on the surface-enhanced Raman scattering (SERS) effect was focused on the cognition of the SERS phenomenon and enhancing its sensitivity for single-molecule detection. With the development of nanomaterials and nanotechnology, the advances and applications based on SERS substrates have been accelerated. Among them, noble metal nanomaterials are mainly used as SERS-active substrates to enhance SERS signals owing to their compelling surface plasmon resonance (SPR) properties. This review provides recent advances, perspectives, and challenges in SERS assays based on engineered noble metal nanomaterials for early cancer diagnosis.

Surface plasmon resonance biosensor for exosome detection based on reformative tyramine signal amplification activated by molecular aptamer beacon

Human epidermal growth factor receptor 2 (HER2)-positive exosomes play an extremely important role in the diagnosis and treatment options of breast cancers. Herein, based on the reformative tyramine signal amplification (TSA) enabled by molecular aptamer beacon (MAB) conversion, a label-free surface plasmon resonance (SPR) biosensor was proposed for highly sensitive and specific detection of HER2-positive exosomes. The exosomes were captured by the HER2 aptamer region of MAB immobilized on the chip surface, which enabled the exposure of the G-quadruplex DNA (G4 DNA) that could form peroxidase-like G4-hemin. In turn, the formed G4-hemin catalyzed the deposition of plentiful tyramine-coated gold nanoparticles (AuNPs-Ty) on the exosome membrane with the help of H₂O₂, generating a significantly enhanced SPR signal. In the reformative TSA system, the horseradish peroxidase (HRP) as a major component was replaced with nonenzymic G4-hemin, bypassing the defects of natural enzymes. Moreover, the dual-recognition of the surface proteins and lipid membrane of the desired exosomes endowed the sensing strategy with high specificity without the interruption of free proteins. As a result, this developed SPR biosensor exhibited a wide linear range from 1.0 × 10⁴ to 1.0 × 10⁷ particles/mL. Importantly, this strategy was able to accurately distinguish HER2-positive breast cancer patients from healthy individuals, exhibiting great potential clinical application.

Insights on functionalized carbon nanotubes for cancer theranostics

Despite the exciting breakthroughs in medical technology, cancer still accounts for one of the principle triggers of death and conventional therapeutic modalities often fail to attain an effective cure. Recently, nanobiotechnology has made huge advancement in cancer therapy with gigantic application potential because of their ability in achieving precise and controlled drug release, elevating drug solubility and reducing adverse effects. Carbon nanotubes (CNTs), one of the most promising carbon-related nanomaterials, have already achieved much success in biomedical field. Due to their excellent optical property, thermal and electronic conductivity, easy functionalization ability and high drug loading capacity, CNTs can be applied in a multifunctional way for cancer treatment and diagnosis. In this review, we will give an overview of the recent progress of CNT-based drug delivery systems in cancer theranostics, which emphasizes their targetability to intracellular components of tumor cells and extracellular elements in tumor microenvironment. Moreover, a detailed introduction on how CNTs penetrate inside the tumor cells to reach their sites of action and achieve the therapeutic effects, as well as their diagnostic applications will be highlighted.

Fabrication of Silver-Decorated Graphene Oxide Nanohybrids via Pulsed Laser Ablation with Excellent Antimicrobial and Optical Limiting Performance

The demand for metallic nanoparticle ornamented nanohybrid materials of graphene oxide (GO) finds copious recognition by virtue of its advanced high-tech applications. Far apart from the long-established synthesis protocols, a novel laser-induced generation of silver nanoparticles (Ag NPs) that are anchored onto the GO layers by a single-step green method named pulsed laser ablation has been exemplified in this work. The second and third harmonic wavelengths (532 nm and 355 nm) of an Nd:YAG pulsed laser is used for the production of Ag NPs from a bulk solid silver target ablated in an aqueous solution of GO to fabricate colloidal Ag-GO nanohybrid materials. UV-Vis absorption spectroscopy, Raman spectroscopy, and TEM validate the optical, structural, and morphological features of the hybrid nanomaterials. The results revealed that the laser-assisted in-situ deposition of Ag NPs on the few-layered GO surface improved its antibacterial properties, in which the hybrid nanostructure synthesized at a longer wavelength exhibited higher antibacterial action resistance to Escherichia coli (E. coli) than Staphylococcus aureus (S. aureus) bacteria. Moreover, nonlinear optical absorption (NLA) of Ag-GO nanohybrid was measured using the open aperture Z-scan technique. The Z-scan results signify the NLA properties of the Ag-GO hybrid material and have a large decline in transmittance of more than 60%, which can be employed as a promising optical limiting (OL) material.

Nanobiotechnology as a platform for the diagnosis of COVID-19: a review

A sensitive method for diagnosing coronavirus disease 2019 (COVID-19) is highly required to fight the current and future global health threats due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV 2). However, most of the current methods exhibited high false‐negative rates, resulting in patient misdiagnosis and impeding early treatment. Nanoparticles show promising performance and great potential to serve as a platform for diagnosing viral infection in a short time and with high sensitivity. This review highlighted the potential of nanoparticles as platforms for the diagnosis of COVID-19. Nanoparticles such as gold nanoparticles, magnetic nanoparticles, and graphene (G) were applied to detect SARS-CoV 2. They have been used for molecular-based diagnosis methods and serological methods. Nanoparticles improved specificity and shorten the time required for the diagnosis. They may be implemented into small devices that facilitate the self-diagnosis at home or in places such as airports and shops. Nanoparticles-based methods can be used for the analysis of virus-contaminated samples from a patient, surface, and air. The advantages and challenges were discussed to introduce useful information for designing a sensitive, fast, and low-cost diagnostic method. This review aims to present a helpful survey for the lesson learned from handling this outbreak to prepare ourself for future  pandemic.

Au-Ag assembled on silica nanoprobes for visual semiquantitative detection of prostate-specific antigen

Background

Blood prostate-specific antigen (PSA) levels are widely used as diagnostic biomarkers for prostate cancer. Lateral-flow immunoassay (LFIA)-based PSA detection can overcome the limitations associated with other methods. LFIAbased PSA detection in clinical samples enables prognosis and early diagnosis owing to the use of high-performance signal reporters.

Results

Here, a semiquantitative LFIA platform for PSA detection in blood was developed using Au–Ag nanoparticles (NPs) assembled on silica NPs (SiO2@Au–Ag NPs) that served as signal reporters. Synthesized SiO2@Au–Ag NPs exhibited a high absorbance at a wide wavelength range (400–800 nm), with a high scattering on nitrocellulose membrane test strips. In LFIA, the color intensity of the test line on the test strip differed depending on the PSA concentration (0.30–10.00 ng/mL), and bands for the test line on the test strip could be used as a standard. When clinical samples were assessed using this LFIA, a visual test line with particular color intensity observed on the test strip enabled the early diagnosis and prognosis of patients with prostate cancer based on PSA detection. In addition, the relative standard deviation of reproducibility was 1.41%, indicating high reproducibility, and the signal reporter showed good stability for 10 days.

Conclusion

These characteristics of the signal reporter demonstrated the reliability of the LFIA platform for PSA detection, suggesting potential applications in clinical sample analysis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00817-4.

A Review of Graphene-Based Surface Plasmon Resonance and Surface-Enhanced Raman Scattering Biosensors: Current Status and Future Prospects

The surface plasmon resonance (SPR) biosensor has become a powerful analytical tool for investigating biomolecular interactions. There are several methods to excite surface plasmon, such as coupling with prisms, fiber optics, grating, nanoparticles, etc. The challenge in developing this type of biosensor is to increase its sensitivity. In relation to this, graphene is one of the materials that is widely studied because of its unique properties. In several studies, this material has been proven theoretically and experimentally to increase the sensitivity of SPR. This paper discusses the current development of a graphene-based SPR biosensor for various excitation methods. The discussion begins with a discussion regarding the properties of graphene in general and its use in biosensors. Simulation and experimental results of several excitation methods are presented. Furthermore, the discussion regarding the SPR biosensor is expanded by providing a review regarding graphene-based Surface-Enhanced Raman Scattering (SERS) biosensor to provide an overview of the development of materials in the biosensor in the future.

Scalable nanolaminated SERS multiwell cell culture assay

This paper presents a new cell culture platform enabling label-free surface-enhanced Raman spectroscopy (SERS) analysis of biological samples. The platform integrates a multilayered metal-insulator-metal nanolaminated SERS substrate and polydimethylsiloxane (PDMS) multiwells for the simultaneous analysis of cultured cells. Multiple cell lines, including breast normal and cancer cells and prostate cancer cells, were used to validate the applicability of this unique platform. The cell lines were cultured in different wells. The Raman spectra of over 100 cells from each cell line were collected and analyzed after 12 h of introducing the cells to the assay. The unique Raman spectra of each cell line yielded biomarkers for identifying cancerous and normal cells. A kernel-based machine learning algorithm was used to extract the high-dimensional variables from the Raman spectra. Specifically, the nonnegative garrote on a kernel machine classifier is a hybrid approach with a mixed nonparametric model that considers the nonlinear relationships between the higher-dimension variables. The breast cancer cell lines and normal breast epithelial cells were distinguished with an accuracy close to 90%. The prediction rate between breast cancer cells and prostate cancer cells reached 94%. Four blind test groups were used to evaluate the prediction power of the SERS spectra. The peak intensities at the selected Raman shifts of the testing groups were selected and compared with the training groups used in the machine learning algorithm. The blind testing groups were correctly predicted 100% of the time, demonstrating the applicability of the multiwell SERS array for analyzing cell populations for cancer research.

Ag and Au nanoparticles/reduced graphene oxide composite materials: Synthesis and application in diagnostics and therapeutics

The exceptional electrical, thermal, optical and mechanical properties have made two dimensional sp² hybridized graphene a material of choice in both academic as well as industrial research. In the last few years, researchers have devoted their efforts towards the development of graphene/polymer, graphene/metal nanoparticle and graphene/ceramic nanocomposites. These materials display excellent mechanical, electrical, thermal, catalytic, magnetic and optical properties which cannot be obtained separately from the individual components. Fascinating physical and chemical properties are displayed by noble metal nanomaterials and thus they represent model building blocks for modifying nanoscale structures for diverse applications extending from catalysis, optics to nanomedicine. Insertion of noble metal (Au, Ag) nanoparticles (NPs) into chemically derived graphene is thus of primary importance to open new avenues for both materials in various fields where the specific properties of each material act synergistically to provide hybrid materials with exceptional performances. This review attempts to summarize the different synthetic procedures for the preparation of Ag and Au NPs/reduced graphene oxide (rGO) composites. The synthesis processes of metal NPs/rGO composites are categorised into in-situ and ex-situ techniques. The in-situ approach consists of simultaneous reduction of metal salts and GO to obtain metal NPs/rGO nanocomposite materials, while in the ex-situ process, the metal NPs of desired size and shape are first synthesized and then transferred onto the GO or rGO matrix. The application of the Ag NPs and Au NPs/rGO composite materials in the area of biomedical (drug delivery and photothermal therapy) and biosensing are the focus of this review article.

Chemical and Bio Sensing Using Graphene-Enhanced Raman Spectroscopy

Graphene is a two-dimensional (2D) material consisting of a single sheet of sp² hybridized carbon atoms laced in a hexagonal lattice, with potentially wide usage as a Raman enhancement substrate, also termed graphene-enhanced Raman scattering (GERS), making it ideal for sensing applications. GERS improves upon traditional surface-enhanced Raman scattering (SERS), combining its single-molecule sensitivity and spectral fingerprinting of molecules, and graphene's simple processing and superior uniformity. This enables fast and highly sensitive detection of a wide variety of analytes. Accordingly, GERS has been investigated for a wide variety of sensing applications, including chemical- and bio-sensing. As a derivative of GERS, the use of two-dimensional materials other than graphene for Raman enhancement has emerged, which possess remarkably interesting properties and potential wider applications in combination with GERS. In this review, we first introduce various types of 2D materials, including graphene, MoS₂, doped graphene, their properties, and synthesis. Then, we describe the principles of GERS and comprehensively explain how the GERS enhancement factors are influenced by molecular and 2D material properties. In the last section, we discuss the application of GERS in chemical- and bio-sensing, and the prospects of such a novel sensing method.

Graphene-based nanoplatforms for surface-enhanced Raman scattering sensing

Surface-enhanced Raman scattering (SERS) is one of the important techniques for sensing applications in biological analysis, disease diagnosis, environmental science, and food safety. Graphene provides an excellent nanoplatform for SERS sensing due to its two-dimensional flat structure, uniform electronic and photonic properties, excellent mechanical stability, atomic uniformity, and high biocompatibility. In this review, we summarize recent advances in the fabrication of various graphene-based nanoplatforms for SERS sensing. We present the strategies, such as self-assembly, in situ synthesis, one-pot synthesis, liquid phase reduction, and biomimetic synthesis, for the fabrication of graphene-based hybrid metallic and alloy nanoplatforms, and then demonstrate the potential applications of graphene-based nanoplatforms for the SERS sensing of ions, organic dyes, pesticides, bacteria, DNA, proteins, cells, and other chemicals in great detail. In addition, we also discuss the future development of this interesting research field and provide several perspectives. This work will be helpful for readers to understand the fabrication and sensing mechanisms of graphene-based SERS sensing nanoplatforms; meanwhile, it will promote the development of new materials and novel methods for high performance sensing and biosensing applications.

Anti-Cancer Drug Sensitivity Assay with Quantitative Heterogeneity Testing Using Single-Cell Raman Spectroscopy

A novel anti-cancer drug sensitivity testing (DST) approach was developed based on in vitro single-cell Raman spectrum intensity (RSI). Generally, the intensity of Raman spectra (RS) for a single living cell treated with drugs positively relates to the sensitivity of the cells to the drugs. In this study, five cancer cell lines (BGC 823, SGC 7901, MGC 803, AGS, and NCI-N87) were exposed to three cytotoxic compounds or to combinations of these compounds, and then they were evaluated for their responses with RSI. The results of RSI were consistent with conventional DST methods. The parametric correlation coefficient for the RSI and Methylthiazolyl tetrazolium assay (MTT) was 0.8558 ± 0.0850, and the coefficient of determination was calculated as R² = 0.9529 ± 0.0355 for fitting the dose⁻response curve. Moreover, RSI data for NCI-N87 cells treated by trastuzumab, everolimus (cytostatic), and these drugs in combination demonstrated that the RSI method was suitable for testing the sensitivity of cytostatic drugs. Furthermore, a heterogeneity coefficient H was introduced for quantitative characterization of the heterogeneity of cancer cells treated by drugs. The largest possible variance between RSs of cancer cells were quantitatively obtained using eigenvalues of principal component analysis (PCA). The ratio of H between resistant cells and sensitive cells was greater than 1.5, which suggested the H-value was effective to describe the heterogeneity of cancer cells. Briefly, the RSI method might be a powerful tool for simple and rapid detection of the sensitivity of tumor cells to anti-cancer drugs and the heterogeneity of their responses to these drugs.

SERS-Active 3D Interconnected Nanocarbon Web toward Nonplasmonic in Vitro Sensing of HeLa Cells and Fibroblasts

A noninvasive intracellular component analysis technique is important in cancer treatment and the initial identification of cancer. Carbon nanomaterials/nanostructures, such as carbon nanotubes and graphene, have little to no surface enhanced Raman scattering (SERS) ability. Because of these structures' low Raman responses, they are conjugated with gold or silver to attain the SERS-active ability to detect normal fibroblasts and HeLa cancer cells. To the best of our knowledge, the effectiveness of the individual use of carbon nanomaterials as a nonplasmonic SERS-active platform for in vitro cancer/normal cell detection has not been investigated to date. Here, for the first time, we introduce a unique nonplasmonic SERS-based biosensing platform that uses a biocompatible self-assembled three-dimensional interconnected nanocarbon web (INW) for in vitro detection and differentiation of HeLa cells and fibroblasts. The sub-10-nm morphology of the INW facilitates the endocytic uptake of INW clusters to the cells, and its SERS functionality introduces live cell Raman sensing. The INW platform has achieved an enhancement factor (EF) of 3.66 × 10⁴ and 9.10 × 10³ with crystal violet and Rhodamine 6G dyes, respectively, significant in comparison to the EF of graphene surfaces (2-17). The results of the time-based Raman spectroscopy of live HeLa cells and fibroblasts revealed chemical fingerprints of intracellular components, such as DNA/RNA, proteins, and lipids. The components' spectroscopic differences facilitate and elucidate the specification of each cell. The highest Raman enhancement achieved was fourfold for fibroblasts (protein) and sixfold for HeLa cells (DNA). Furthermore, the SERS spectra along with scanning electron microscopy and fluorescence microscopy analysis of the immobilized cells after 24 and 48 h shed light on the health of fibroblasts and HeLa cells. A photon energy-induced ionization achieved with a femtosecond laser fabricated a biocompatible INW platform with the designated unique attributes. This simple, label-free, in vitro diagnosis approach for HeLa cells and fibroblasts has strong potential for cancer research.

Ultrasonicated graphene oxide enhances bone and skin wound regeneration

In the present study, we investigated the applications of ultrasonicated graphene oxide (UGO) for bone regeneration and skin wound healing. Ultrasonication of a GO suspension increased the dispersion and stability (by increasing the zeta potential) of the GO suspension. UGO has fewer oxygen-containing groups but still displays excellent water dispersion. The UGO supension showed high biocompatibility for human fetal osteoblast (hFOB cells), human endothelial cells (EA.hy 926 cells), and mouse embryonic fibroblasts. Importantly, UGO could support cell attachment and proliferation, in addition to promoting the osteogenesis of seeded cells and the promotion of new bone formation. In addition, a 1% UGO supension enhanced cell migration in an in vitro skin scratch assay and promoted wound closure in an in vivo rat excisional skin defect model. These results showed that UGO offers a good environment for cells involved in bone and skin healing, suggesting its potential application in tissue regeneration.

State of the art and recent advances in the ultrasound-assisted synthesis, exfoliation and functionalization of graphene derivatives

Sonochemistry, an almost a century old technique was predominantly employed in the cleaning and extraction processes but this tool has now slowly gained tremendous attention in the synthesis of nanoparticles (NPs) where particles of sub-micron have been produced with great stability. Following this, ultrasonication techniques have been largely employed in graphene synthesis and its dispersion in various solvents which would conventionally take days and offers poor yield. Ultrasonic irradiation allows the production of thin-layered graphene oxide (GO) and reduced graphene oxide (RGO) of up to 1nm thickness and can be produced in single layers. With ultrasonic treatment, reactions were made easy whereby graphite can be directly exfoliated to graphene layers. Oxidation to GO can also be carried out within minutes and reduction to RGO is possible without the use of any reducing agents. In addition, various geometry of graphene can be produced such as scrolled graphene, sponge or foam graphene, smooth as well as those with rough edges, each serving its own unique purpose in various applications such as supercapacitor, catalysis, biomedical, etc. In ultrasonic-assisted reaction, deposition of metal NPs on graphene was more homogeneous with custom-made patterns such as core-shell formation, discs, clusters and specific deposition at the edges of graphene sheets. Graphene derivatives with the aid of ultrasonication are the perfect catalyst for various organic reactions as well as an excellent adsorbent. Reactions which used to take hours and days were significantly reduced to minutes with exceedingly high yields. In a more recent approach, sonophotocatalysis was employed for the combined effect of sonication and photocatalysis of metal deposited graphene. The system was highly efficient in organic dye adsorption. This review provides detailed fundamental concepts of ultrasonochemistry for the synthesis of graphene, its dispersion, exfoliation as well as its functionalization, with great emphasis only based on recent publications. Necessary parameters of sonication such as frequency, power input, sonication time, type of sonication as well as temperature and dual-frequency sonication are discussed in great length to provide an overview of the resultant graphene products.

Applications of vitamin B6 cofactor pyridoxal 5'-phosphate and pyridoxal 5'-phosphate crowned gold nanoparticles for optical sensing of metal ions

Vitamin B6 cofactor pyridoxal 5'-phosphate (PLP) and PLP crowned gold nanoparticles (PLP-AuNPs) was applied for the optical chemosensing of metal ions in aqueous medium. PLP showed a visually detectable colour change from colourless to yellow and 'turn-off' fluorescence in the presence of Fe³⁺. The fluorescence intensity of PLP at 433nm was also blue-shifted and enhanced at 395nm upon addition of Al³⁺. When the PLP was functionalized over AuNPs surface, the wine red colour of PLP-AuNPs was turned to purplish-blue and the SPR band at ~525nm was red-shifted upon addition of Al³⁺, Cd²⁺ and Pb²⁺ due to the complexation-induced aggregation of nanoparticles. The developed sensing systems exhibited good selectivity and specificity for the detected analytes (Fe³⁺, Al³⁺, Cd²⁺ and Pb²⁺).

SERS Active Nanobiosensor Functionalized by Self-Assembled 3D Nickel Nanonetworks for Glutathione Detection

We introduce a "non-noble metal" based SERS active nanobiosensor using a self-assembled 3D hybrid nickel nanonetwork. A tunable biomolecule detector fabricated by a bottom-up approach was functionalized using a multiphoton ionization energy mechanism to create a self-assembled 3D hybrid nickel nanonetwork. The nanonetwork was tested for SERS detection of crystal violet (CV) and glutathione (GSH) at two excitation wavelengths, 532 and 785 nm. The results reveal indiscernible peaks with a limit of detection (LOD) of 1 picomolar (pM) concentration. An enhancement factor (EF) of 9.3 × 10⁸ was achieved for the chemical molecule CV and 1.8 × 10⁹ for the biomolecule GSH, which are the highest reported values so far. The two results, one being the CV molecule proved that nickel nanonetwork is indeed SERS active and the second being the GSH biomolecule detection at both 532 and 785 nm, confirm that the nanonetwork is a biosensor which has potential for both in vivo and in vitro sensing. In addition, the selectivity and versatility of this biosensor is examined with biomolecules such as l-Cysteine, l-Methionine, and sensing GSH in cell culture medium which mimics the complex biological environment. The functionalized self-assembled 3D hybrid nickel nanonetwork exhibits electromagnetic and charge transfer based SERS activation mechanisms.

Sonochemical and sustainable synthesis of graphene-gold (G-Au) nanocomposites for enzymeless and selective electrochemical detection of nitric oxide

In this study, a sonochemical approach was utilised for the development of graphene-gold (G-Au) nanocomposite. Through the sonochemical method, simultaneous exfoliation of graphite and the reduction of gold chloride occurs to produce highly crystalline G-Au nanocomposite. The in situ growth of gold nanoparticles (AuNPs) took place on the surface of exfoliated few-layer graphene sheets. The G-Au nanocomposite was characterised by UV-vis, XRD, FTIR, TEM, XPS and Raman spectroscopy techniques. This G-Au nanocomposite was used to modify glassy carbon electrode (GCE) to fabricate an electrochemical sensor for the selective detection of nitric oxide (NO), a critical cancer biomarker. G-Au modified GCE exhibited an enhanced electrocatalytic response towards the oxidation of NO as compared to other control electrodes. The electrochemical detection of NO was investigated by linear sweep voltammetry analysis, utilising the G-Au modified GCE in a linear range of 10-5000μM which exhibited a limit of detection of 0.04μM (S/N=3). Furthermore, this enzyme-free G-Au/GCE exhibited an excellent selectivity towards NO in the presence of interferences. The synergistic effect of graphene and AuNPs, which facilitated exceptional electron-transfer processes between the electrolyte and the GCE thereby improving the sensing performance of the fabricated G-Au modified electrode with stable and reproducible responses. This G-Au nanocomposite introduces a new electrode material in the sensitive and selective detection of NO, a prominent biomarker of cancer.

Biosensors for breast cancer diagnosis: A review of bioreceptors, biotransducers and signal amplification strategies

Breast cancer is highly prevalent in females and accounts for second highest number of deaths, worldwide. Cumbersome, expensive and time consuming detection techniques presently available for detection of breast cancer potentiates the need for development of novel, specific and ultrasensitive devices. Biosensors are the promising and selective detection devices which hold immense potential as point of care (POC) tools. Present review comprehensively scrutinizes various breast cancer biosensors developed so far and their technical evaluation with respect to efficiency and potency of selected bioreceptors and biotransducers. Use of glycoproteins, DNA biomarkers, micro-RNA, circulatory tumor cells (CTC) and some potential biomarkers are introduced briefly. The review also discusses various strategies used in signal amplification such as nanomaterials, redox mediators, p19 protein, duplex specific nucleases (DSN) and redox cycling.

Graphene-Gold Nanoparticles Hybrid-Synthesis, Functionalization, and Application in a Electrochemical and Surface-Enhanced Raman Scattering Biosensor

Graphene is a single-atom-thick two-dimensional carbon nanosheet with outstanding chemical, electrical, material, optical, and physical properties due to its large surface area, high electron mobility, thermal conductivity, and stability. These extraordinary features of graphene make it a key component for different applications in the biosensing and imaging arena. However, the use of graphene alone is correlated with certain limitations, such as irreversible self-agglomerations, less colloidal stability, poor reliability/repeatability, and non-specificity. The addition of gold nanostructures (AuNS) with graphene produces the graphene-AuNS hybrid nanocomposite which minimizes the limitations as well as providing additional synergistic properties, that is, higher effective surface area, catalytic activity, electrical conductivity, water solubility, and biocompatibility. This review focuses on the fundamental features of graphene, the multidimensional synthesis, and multipurpose applications of graphene-Au nanocomposites. The paper highlights the graphene-gold nanoparticle (AuNP) as the platform substrate for the fabrication of electrochemical and surface-enhanced Raman scattering (SERS)-based biosensors in diverse applications as well as SERS-directed bio-imaging, which is considered as an emerging sector for monitoring stem cell differentiation, and detection and treatment of cancer.

Green and Tunable Decoration of Graphene with Spherical Nanoparticles Based on Laser Ablation in Water: A Case of Ag Nanoparticle/Graphene Oxide Sheet Composites

A simple and green strategy is presented to decorate graphene with nanoparticles, based on laser ablation of targets in graphene auqeous solution. Ag and graphene oxide (GO) are chosen as model materials. The surface of GO sheets is strongly anchored with spherical Ag nanoparticles. The density and size of the Ag nanoparticles can be easily tuned by laser ablation conditions. Further, the GO sheets can be decorated with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. Additionally, the Ag nanoparticle/GO sheet colloids can be utilized as blocks to build three-dimensional structures, such as sandwich membranes by evaporation-induced self-assembly. These graphene-based composite materials could be very useful in catalysis, sensors, and nanodevices. Particularly, the Ag nanoparticle/GO sheet sandwich composite membranes exhibit excellent surface-enhanced Raman scattering performance and possess the huge potential in trace-detecting persistent organic pollutants in the environment.

Graphene: The Missing Piece for Cancer Diagnosis?

This paper reviews recent advances in graphene-based biosensors development in order to obtain smaller and more portable devices with better performance for earlier cancer detection. In fact, the potential of Graphene for sensitive detection and chemical/biological free-label applications results from its exceptional physicochemical properties such as high electrical and thermal conductivity, aspect-ratio, optical transparency and remarkable mechanical and chemical stability. Herein we start by providing a general overview of the types of graphene and its derivatives, briefly describing the synthesis procedure and main properties. It follows the reference to different routes to engineer the graphene surface for sensing applications with organic biomolecules and nanoparticles for the development of advanced biosensing platforms able to detect/quantify the characteristic cancer biomolecules in biological fluids or overexpressed on cancerous cells surface with elevated sensitivity, selectivity and stability. We then describe the application of graphene in optical imaging methods such as photoluminescence and Raman imaging, electrochemical sensors for enzymatic biosensing, DNA sensing, and immunosensing. The bioquantification of cancer biomarkers and cells is finally discussed, particularly electrochemical methods such as voltammetry and amperometry which are generally adopted transducing techniques for the development of graphene based sensors for biosensing due to their simplicity, high sensitivity and low-cost. To close, we discuss the major challenges that graphene based biosensors must overcome in order to reach the necessary standards for the early detection of cancer biomarkers by providing reliable information about the patient disease stage.

Biosensors and nanobiosensors for therapeutic drug and response monitoring

Review of different biosensors and nanobiosensors increasingly used in therapeutic drug monitoring (TDM) for pharmaceutical drugs with dosage limitations or toxicity issues and for therapeutic response monitoring.

Lighting up the Raman signal of molecules in the vicinity of graphene related materials

Surface enhanced Raman scattering (SERS) is a popular technique to detect the molecules with high selectivity and sensitivity. It has been developed for 40 years, and many reviews have been published to summarize the progress in SERS. Nevertheless, how to make the SERS signals repeatable and quantitative and how to have deeper understanding of the chemical enhancement mechanism are two big challenges. A strategy to target these issues is to develop a Raman enhancement substrate that is flat and nonmetal to replace the conventional rough and metal SERS substrate. At the same time, the newly developed substrate should have a strong interaction with the adsorbate molecules to guarantee strong chemical enhancement. The flatness of the surface allows better control of the molecular distribution and configuration, while the nonmetal surface avoids disturbance of the electromagnetic mechanism. Recently, graphene and other two-dimensional (2D) materials, which have an ideal flat surface and strong chemical interaction with plenty of organic molecules, were developed to be used as Raman enhancement substrates, which can light up the Raman signals of the molecules, and these substrates were demonstrated to be a promising for microspecies or trace species detection. This effect was named "graphene enhanced Raman scattering (GERS)". The GERS technique offers significant advantages for studying molecular vibrations due to the ultraflat and chemically inert 2D surfaces, which are newly available, especially in developing a quantitative and repeatable signal enhancement technique, complementary to SERS. Moreover, GERS is a chemical mechanism dominated effect, which offers a valuable model to study the details of the chemical mechanism. In this Account, we summarize the systematic studies exploring the character of GERS. In addition, as a practical technique, the combination of GERS with a metal substrate incorporates the advantages from both conventional SERS and GERS. The introduction of graphene to the Raman enhancement substrate extended SERS applications in a more controllable and quantitative way. Looking to the future, we expect the combination of the SERS concept with the GERS technology to lead to the solution of some important issues in chemical dynamics and in biological processes monitoring.

Molecular selectivity of graphene-enhanced Raman scattering

Graphene-enhanced Raman scattering (GERS) is a recently discovered Raman enhancement phenomenon that uses graphene as the substrate for Raman enhancement and can produce clean and reproducible Raman signals of molecules with increased signal intensity. Compared to conventional Raman enhancement techniques, such as surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS), in which the Raman enhancement is essentially due to the electromagnetic mechanism, GERS mainly relies on a chemical mechanism and therefore shows unique molecular selectivity. In this paper, we report graphene-enhanced Raman scattering of a variety of different molecules with different molecular properties. We report a strong molecular selectivity for the GERS effect with enhancement factors varying by as much as 2 orders of magnitude for different molecules. Selection rules are discussed with reference to two main features of the molecule, namely its molecular energy levels and molecular structures. In particular, the enhancement factor involving molecular energy levels requires the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies to be within a suitable range with respect to graphene's Fermi level, and this enhancement effect can be explained by the time-dependent perturbation theory of Raman scattering. The enhancement factor involving the choice of molecular structures indicates that molecular symmetry and substituents similar to that of the graphene structure are found to be favorable for GERS enhancement. The effectiveness of these factors can be explained by group theory and the charge-transfer interaction between molecules and graphene. Both factors, involving the molecular energy levels and structural symmetry of the molecules, suggest that a remarkable GERS enhancement requires strong molecule-graphene coupling and thus effective charge transfer between the molecules and graphene. These conclusions are further experimentally supported by the change of the UV-visible absorption spectra of molecules when in contact with graphene and these conclusions are theoretically corroborated by first-principles calculations. These research findings are important for gaining fundamental insights into the graphene-molecule interaction and the chemical mechanism in Raman enhancement, as well as for advancing the role of such understanding both in guiding chemical and molecule detection applications and in medical and biological technology developments.