Surface-Enhanced Raman Scattering-Based Sensing In Vitro: Facile and Label-Free Detection of Apoptotic Cells at the Single-Cell Level

From Genotype to Phenotype: Raman Spectroscopy and Machine Learning for Label-Free Single-Cell Analysis

Raman spectroscopy has made significant progress in biosensing and clinical research. Here, we describe how surface-enhanced Raman spectroscopy (SERS) assisted with machine learning (ML) can expand its capabilities to enable interpretable insights into the transcriptome, proteome, and metabolome at the single-cell level. We first review how advances in nanophotonics-including plasmonics, metamaterials, and metasurfaces-enhance Raman scattering for rapid, strong label-free spectroscopy. We then discuss ML approaches for precise and interpretable spectral analysis, including neural networks, perturbation and gradient algorithms, and transfer learning. We provide illustrative examples of single-cell Raman phenotyping using nanophotonics and ML, including bacterial antibiotic susceptibility predictions, stem cell expression profiles, cancer diagnostics, and immunotherapy efficacy and toxicity predictions. Lastly, we discuss exciting prospects for the future of single-cell Raman spectroscopy, including Raman instrumentation, self-driving laboratories, Raman data banks, and machine learning for uncovering biological insights.

Highly Sensitive Microarray Immunoassay for Multiple Mycotoxins on Engineered 3D Porous Silicon SERS Substrate with Silver Nanoparticle Magnetron Sputtering

A high-throughput, rapid, and highly sensitive surface-enhanced Raman spectroscopy (SERS) microarray for screening multiple mycotoxins has been developed on a three-dimensional silver nanoparticle porous silicon (3D AgNP-Psi) SERS substrate, which was easy to be engineered by electrochemical etching and magnetron sputtering technology. The etching current density, etching waveform, and target material for magnetron sputtering have been investigated to obtain an optimal 3D SERS substrate. The optimized 3D AgNP-Psi SERS substrate showed an enhancement factor of 2.3 × 107 at 400 mA/cm2 constant current density etching for 20 s and Ag target magnetron sputtering for 200 nm thickness on the surface of Psi. The simulation electric field distribution showed the near-field enhancement can reach 3× higher than that of AuNPs. A protein microarray has been designed to screen multiple mycotoxins by AuNP Raman tags and a competitive immunoassay protocol on the surface of the 3D SERS substrate. The SERS protein microarray displayed wide linear detection ranges of 0.001-100 ng/mL for ochratoxin A, 0.01-100 ng/mL for aflatoxin B1, 0.001-10 ng/mL for deoxynivalenol, along with pg/mL low limit of detection, good recovery rates, repeatability, and reproducibility. The 3D SERS protein microarray is easily engineered and has a great potential application in medicine, environment, and food industry fields.

Alveoli-Like Multifunctional Scaffolds for Optical and Electrochemical In Situ Monitoring of Cellular Responses from Type II Pneumocytes

While breathing, alveoli are exposed to external irritants, which contribute to the pathogenesis of lung disease. Therefore, in situ monitoring of alveolar responses to stimuli of toxicants under in vivo environments is important to understand lung disease. For this purpose, 3D cell cultures are recently employed for examining cellular responses of pulmonary systems exposed to irritants; however, most of them have used ex situ assays requiring cell lysis and fluorescent labeling. Here, an alveoli-like multifunctional scaffold is demonstrated for optical and electrochemical monitoring of cellular responses of pneumocytes. Porous foam with dimensions like the alveoli structure is used as a backbone for the scaffold, wherein electroactive metal-organic framework crystals, optically active gold nanoparticles, and biocompatible hyaluronic acid are integrated. The fabricated multifunctional scaffold allows for label-free detection and real-time monitoring of oxidative stress released in pneumocytes under toxic-conditions via redox-active amperometry and nanospectroscopy. Moreover, cellular behavior can be statistically classified based on fingerprint Raman signals collected from the cells on the scaffold. The developed scaffold is expected to serve as a promising platform to investigate cellular responses and disease pathogenesis, owing to its versatility in monitoring electrical and optical signals from cells in situ in the 3D microenvironments.

LANCE: a Label-Free Live Apoptotic and Necrotic Cell Explorer Using Convolutional Neural Network Image Analysis

Identifying and quantifying cell death is the basis for all cell death research. Current methods for obtaining these quantitative measurements rely on established biomarkers, yet the marker-based approach suffers from limited marker specificity, high cost of reagents, lengthy sample preparation, and fluorescence imaging. Based on the morphological difference, we developed a Live, Apoptotic, and Necrotic Cell Explorer (LANCE) to categorize cell death status in a label-free manner, by incorporating machine learning and image processing. The LANCE workflow includes cropping individual cells from microscopic images having hundreds of cells, formation of an image database of around 5000 events, training and validation of the convolutional neural network models using multiple cell lines, and treatment conditions. With LANCE, we precisely categorized live, apoptotic, and necrotic cells with a high accuracy of 96.3 ± 0.5%. More importantly, the nondestructive label-free LANCE method allows for tracking time dynamics of the cell death process, which enhances the understanding of subtle cell death regulation at the molecular level. Hence, LANCE is a fast, low-cost, and nondestructive label-free method to distinguish cell status, which can be applied to cell death studies as well as many other biomedical applications.

Large-area metal-dielectric heterostructures for surface-enhanced raman scattering

Metal-dielectric heterostructures have shown great application potentials in physics, chemistry and material science. In this work, we have designed and manufactured ordered metal-dielectric multiple heterostructures with tunable optical properties, which can be as large as the order of square centimeters in size. We experimentally realized that the surface-enhanced Raman scattering signal of the periodic multiple heterostructures increased 50 times compared with the silicon nanodisk-gold film arrays, which is attributed to the large-scale hotspots and high efficient coupling between the optical cavities and surface plasmon resonance modes. More importantly, the substrate also features a good uniformity and an excellent reproducible fabrication, which is very promising for practical applications.

A review of surface-enhanced Raman spectroscopy in pathological processes

With the continuous growth of the human population and new challenges in the quality of life, it is more important than ever to diagnose diseases and pathologies with high accuracy, sensitivity and in different scenarios from medical implants to the operation room. Although conventional methods of diagnosis revolutionized healthcare, alternative analytical methods are making their way out of academic labs into clinics. In this regard, surface-enhanced Raman spectroscopy (SERS) developed immensely with its capability to achieve single-molecule sensitivity and high-specificity in the last two decades, and now it is well on its way to join the arsenal of physicians. This review discusses how SERS is becoming an essential tool for the clinical investigation of pathologies including inflammation, infections, necrosis/apoptosis, hypoxia, and tumors. We critically discuss the strategies reported so far in nanoparticle assembly, functionalization, non-metallic substrates, colloidal solutions and how these techniques improve SERS characteristics during pathology diagnoses like sensitivity, selectivity, and detection limit. Moreover, it is crucial to introduce the most recent developments and future perspectives of SERS as a biomedical analytical method. We finally discuss the challenges that remain as bottlenecks for a routine SERS implementation in the medical room from in vitro to in vivo applications. The review showcases the adaptability and versatility of SERS to resolve pathological processes by covering various experimental and analytical methods and the specific spectral features and analysis results achieved by these methods.

Elucidating Gold-MnO2 Core-Shell Nanoenvelope for Real Time SERS-Guided Photothermal Therapy on Pancreatic Cancer Cells

Pancreatic cancer represents one of the most aggressive in nature with a miserable prognosis that warrants efficient diagnostic and therapeutic interventions. Herein, a MnO₂ overlaid gold nanoparticle (AuNPs) based photothermal theranostic nanoenvelope (PTTNe:MnO₂@AuNPs) was fabricated to substantiate surface-enhanced Raman spectroscopy (SERS) guided real-time monitoring of photothermal therapy (PTT) in pancreatic cancer cells. A sharp enhancement of the fingerprint Raman signature of MnO₂ at 569 cm^-1 exhibited as a marker peak for the first time to elucidate the intracellular PTT event. In this strategic design, the leftover bare AuNPs after the degradation of the MnO₂ layer from the nanoenvelope in the presence of intracellular H₂O₂ enabled real-time tracking of biomolecular changes of Raman spectral variations during PTT. Moreover, the surface of the as-synthesized nanoenvelope was functionalized with a pancreatic cancer cell targeting peptide sequence for cholecystokinin fashioned the PTTNe with admirable stability and biocompatibility. Finally, the precise cell death mechanism was explicitly assessed by SERS spectral analysis as a complementary technique. This targeted phototheranostic approach demonstrated in pancreatic cancer cells presented a therapeutically viable prototype for futuristic personalized cancer nanomedicine.

Sub-10 nm Nanolaminated Al2O3/HfO2 Coatings for Long-Term Stability of Cu Plasmonic Nanodisks in Physiological Environments

By supporting localized plasmon modes, metal-based plasmonic nanostructures can confine optical fields at deep-subwavelength scale in various applications, such as biological and chemical sensing, nanoscale light emission, and solar energy harvesting. While Cu is a low-cost complementary metal oxide semiconductor (CMOS) compatible material, its poor chemical stability limits the use of Cu plasmonic nanodevices in corrosive biochemical aqueous environments. In this paper, we demonstrate that sub-10 nm Al₂O₃/HfO₂ nanolaminated coatings can significantly extend the lifetime of Cu nanodisk arrays from ∼5 h to ∼180 days in the physiological environment of 1× phosphate-buffered saline (PBS) at 37 °C. Cu nanodisk arrays are fabricated using freestanding Au nanohole array films as the physical vapor deposition masks and sub-10 nm nanolaminated coatings composed of alternating Al₂O₃ and HfO₂ nanolayers are grown on Cu nanodisk arrays by atomic layer deposition (ALD). Time-dependent optical extinction measurements of Cu nanodisk arrays are conducted in 1× solutions at 37 °C to investigate the anticorrosion performance for different pure and nanolaminated ALD coatings. We observe a linear relationship between the lifetime of Cu nanodisk arrays in 1× PBS at 37 °C and the nanolaminated coating thickness, and ∼1.3 nm nanolaminated coatings of ∼10 ALD cycles can extend the lifetime of Cu plasmonics up to ∼20 days. Furthermore, we find that the anticorrosion performance of Al₂O₃/HfO₂ nanolaminated ALD coatings strongly depends on the processing and the geometric parameters, such as the annealing temperature and the nanolaminated backbone unit size.

Application of random forest based approaches to surface-enhanced Raman scattering data

Surface-enhanced Raman scattering (SERS) is a valuable analytical technique for the analysis of biological samples. However, due to the nature of SERS it is often challenging to exploit the generated data to obtain the desired information when no reporter or label molecules are used. Here, the suitability of random forest based approaches is evaluated using SERS data generated by a simulation framework that is also presented. More specifically, it is demonstrated that important SERS signals can be identified, the relevance of predefined spectral groups can be evaluated, and the relations of different SERS signals can be analyzed. It is shown that for the selection of important SERS signals Boruta and surrogate minimal depth (SMD) and for the analysis of spectral groups the competing method Learner of Functional Enrichment (LeFE) should be applied. In general, this investigation demonstrates that the combination of random forest approaches and SERS data is very promising for sophisticated analysis of complex biological samples.

Size-dependent apoptotic activity of gold nanoparticles on osteosarcoma cells correlated with SERS signal

In the last decade, gold nanoparticles have emerged as promising agents for in vitro bio-sensing and in vivo cancer theranostics. However, different investigations have reported widely varying cytotoxicity and uptake efficiency of gold nanoparticles depending upon their size. Therefore, more extensive studies are needed to standardize these biological effects as a function of size on a particular cell line. In addition, to obtain robust confirmation on the correlation of a size to biological effect, thorough mechanistic study must also be performed. In this study, the size dependent biological activities of gold nanoparticles on osteosarcoma cells is investigated towards exploring their potential theranostic application in bone cancer, for which very scarce literature reports are available. Tris-assisted citrate based method was optimized to synthesize stable gold naoparticles of 40-60 nm sizes. Nanoparticles were characterized through UV-Vis spectroscopy, field emission scanning electron microscope (FESEM) and dynamic light scattering (DLS). Increasing concentrations of gold nanoparticles (AuNPs) of 46 nm size, enhanced the rate of reactive oxygen species (ROS)-induced apoptosis in MG63 cells by disrupting their mitochondrial membrane potential. Considerably higher cell death was observed for 46 and 60 nm AuNPs compared to 38 nm at all concentrations of 200, 400 and 800 ng/mL. Further, molecular signatures of cellular apoptosis under nanoparticle treatment were optically assessed through surface enhanced Raman scattering (SERS). A significant Raman enhancement in cancer cells under treatment of larger gold nanoparticles (46 and 60 nm) at fixed wavelength of 785 nm and laser power of 8.0 mW was evident. In corroboration with molecular biology techniques, SERS observation confirmed the size-dependent apoptotic phenomena in osteosarcoma cells under treatment of gold nanoparticles. Study demonstrates a facile, non-active targeting approach for detection of size-dependent AuNP-induced apoptosis in osteosarcoma cells through label-free SERS method.

Refractive-Index-Insensitive Nanolaminated SERS Substrates for Label-Free Raman Profiling and Classification of Living Cancer Cells

Surface-enhanced Raman spectroscopy (SERS) has emerged as an ultrasensitive molecular-fingerprint-based technique for label-free biochemical analysis of biological systems. However, for conventional SERS substrates, SERS enhancement factors (EFs) strongly depend on background refractive index (RI), which prevents reliable spatiotemporal SERS analysis of living cells consisting of different extra-/intracellular organelles with a heterogeneous distribution of local RI values between 1.30 and 1.60. Here, we demonstrate that nanolaminated SERS substrates can support uniform arrays of vertically oriented nanogap hot spots with large SERS EFs (>10⁷) insensitive to background RI variations. Experimental and numerical studies reveal that the observed RI-insensitive SERS response is due to the broadband multiresonant optical properties of nanolaminated plasmonic nanostructures. As a proof-of-concept demonstration, we use RI-insensitive nanolaminated SERS substrates to achieve label-free Raman profiling and classification of living cancer cells with a high prediction accuracy of 96%. We envision that RI-insensitive high-performance nanolaminated SERS substrates can potentially enable label-free spatiotemporal biochemical analysis of living biological systems.

Tracing Size and Surface Chemistry-Dependent Endosomal Uptake of Gold Nanoparticles Using Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS)-based single-cell analysis is an emerging approach to obtain molecular level information from molecular dynamics in a living cell. In this study, endosomal biochemical dynamics was investigated based on size and surface chemistry-dependent uptake of gold nanoparticles (AuNPs) on single cells over time using SERS. MDA-MB-231 breast cancer cells were exposed to 13 and 50 nm AuNPs and their polyadenine oligonucleotide-modified forms by controlling the order and combination of AuNPs. The average spectra obtained from 20 single cells were analyzed to study the nature of the biochemical species or processes taking place on the AuNP surfaces. The spectral changes, especially from proteins and lipids of endosomal vesicles, were observed depending on the size, surface chemistry, and combination as well as the duration of the AuNP treatment. The results demonstrate that SERS spectra are sensitive to trace biochemical changes not only the size, surface chemistry, and aggregation status of AuNPs but also the endosomal maturation steps over time, which can be simple and fast way for understanding the AuNP behavior in single cell and useful for the assisting and controlling of AuNP-based gene or drug delivery applications.

Exploring the margins of SERS in practical domain: An emerging diagnostic modality for modern biomedical applications

Excellent multiplexing capability, molecular specificity, high sensitivity and the potential of resolving complex molecular level biological compositions augmented the diagnostic modality of surface-enhanced Raman scattering (SERS) in biology and medicine. While maintaining all the merits of classical Raman spectroscopy, SERS provides a more sensitive and selective detection and quantification platform. Non-invasive, chemically specific and spatially resolved analysis facilitates the exploration of SERS-based nano probes in diagnostic and theranostic applications with improved clinical outcomes compared to the currently available so called state-of-art technologies. Adequate knowledge on the mechanism and properties of SERS based nano probes are inevitable in utilizing the full potential of this modality for biomedical applications. The safety and efficiency of metal nanoparticles and Raman reporters have to be critically evaluated for the successful translation of SERS in to clinics. In this context, the present review attempts to give a comprehensive overview about the selected medical, biomedical and allied applications of SERS while highlighting recent and relevant outcomes ranging from simple detection platforms to complicated clinical applications.

Paper-Based Surface-Enhanced Raman Spectroscopy for Diagnosing Prenatal Diseases in Women

We report the development of a surface-enhanced Raman spectroscopy sensor chip by decorating gold nanoparticles (AuNPs) on ZnO nanorod (ZnO NR) arrays vertically grown on cellulose paper (C). We show that these chips can enhance the Raman signal by 1.25 × 10⁷ with an excellent reproducibility of <6%. We show that we can measure trace amounts of human amniotic fluids of patients with subclinical intra-amniotic infection (IAI) and preterm delivery (PTD) using the chip in combination with a multivariate statistics-derived machine-learning-trained bioclassification method. We can detect the presence of prenatal diseases and identify the types of diseases from amniotic fluids with >92% clinical sensitivity and specificity. Our technology has the potential to be used for the early detection of prenatal diseases and can be adapted for point-of-care applications.

Silicon Nanomaterials for Biosensing and Bioimaging Analysis

Biochemical analysis in reliable, low-toxicity, and real-time manners are essentially important for exploring and unraveling biological events and related mechanisms. Silicon nanomaterial-based sensors and probes have potentiality to satisfy the above-mentioned requirements. Herein, we present an overview of the recent significant improvement in large-scale and facile synthesis of high-quality silicon nanomaterials and the research progress of biosensing and bioimaging analysis based on silicon nanomaterials. We especially illustrate the advanced applications of silicon nanomaterials in the field of ultrasensitive biomolecular detection and dynamic biological imaging analysis, with a focus on real-time and long-term detection. In the final section of this review, we discuss the major challenges and promising development in this domain.

Silicon nanohybrid-based SERS chips armed with an internal standard for broad-range, sensitive and reproducible simultaneous quantification of lead(ii) and mercury(ii) in real systems

Lead ions (Pb²⁺) and mercury ions (Hg²⁺), the two commonly coexisting heavy metal ions, pose severe risks to environment and human health. To date, no surface-enhanced Raman scattering (SERS) sensor has been reported for the simultaneous quantification of Pb²⁺ and Hg²⁺ in real systems. Herein, the first demonstration of SERS chips for simultaneous quantification of Pb²⁺ and Hg²⁺ in real systems is presented based on the combination of reproducible silicon nanohybrid substrates and a corrective internal standard (IS) sensing strategy. This chip was made of a silver nanoparticle-decorated silicon wafer via modification of the IS, i.e. 4-aminothiophenol, molecules. The as-prepared chip was further functionalized with Pb²⁺- and Hg²⁺- specific DNA strands capable of simultaneously detecting Pb²⁺ and Hg²⁺. Quantitatively, upon correction by the IS Raman signals, the broad dynamic ranges from 100 pM to 10 μM for Pb²⁺ and from 1 nM to 10 μM for Hg²⁺ were achieved, with the detection limit down to 19.8 ppt for Pb²⁺ and 168 ppt for Hg²⁺. For real applications, we further demonstrated that Pb²⁺ and Hg²⁺ spiked into industrial wastewater could be readily distinguished via the presented chip, and the relative standard deviation (RSD) value was less than ∼15%. More significantly, the resulting SERS chip can be well coupled with a hand-held Raman instrument and can then be used for the qualitative analysis of both Pb²⁺ and Hg²⁺ in real systems in a portable manner. Our results suggest that this high-quality SERS chip is a powerful tool for on-site detection of various heavy metal ions in real samples in the field of food safety and environment protection.

Rational synthesis of hollow cubic CuS@Spiky Au core–shell nanoparticles for enhanced photothermal and SERS effects

The unique “tip spots” can simultaneously enhance SERS and the photothermal effect, facilitating label-free SERS intracellular imaging during cell apoptosis.

Common Aspects Influencing the Translocation of SERS to Biomedicine

This review overviews the impact in biomedicine of surface enhanced. Raman scattering motivated by the great potential we believe this technique has. We present the advantages and limitations of this technique relevant to bioanalysis in vitro and in vivo and how this technique goes beyond the state of the art of traditional analytical, labelling and healthcare diagnostic technologies.

A Critical Review on Ultrasensitive, Spectroscopic-based Methods for High-throughput Monitoring of Bacteria during Infection Treatment

The world is in the midst of a pre-emptive public health emergency, one that is just as dramatic as the global aggressive viruses-related crises (Ebola, Zika, or SARS), but not as visible. The "superbugs" and their antimicrobial resistance do not cause much public alarm or awareness, but provoke financial losses of $100 trillion annually (WHO, http://www.who.int/mediacentre/commentaries/superbugs-action-now/en/ ). This status quo review offers an overview of ultrasensitive methods for high-throughput monitoring of bacteria during infection treatment, the effects of antibiotics on bacteria at single-cell level and the challenges we will face in their detection due to the extraordinary capability of these "superbugs" to gain and constantly improve multiresistance to antibiotics. A special emphasis is put on the ultrasensitive spectroscopic-based analysis techniques, using nanotechnology or not necessarily, that are more and more promising alternatives to conventional culture-based ones. The particular case of Mycobacteria detection is discussed based on recent reported work.

Biocompatible 3D SERS substrate for trace detection of amino acids and melamine

A novel, low-cost and biocompatible three-dimensional (3D) substrate for surface-enhanced Raman spectroscopy (SERS) is fabricated using gold nanoparticles (AuNPs) loaded on cellulose paper for detection of amino acids and melamine. Dysosma pleiantha rhizome (Dp-Rhi) capped AuNPs (Dp-Rhi_AuNPs) were prepared by in situ using aqueous extract of Dp-Rhi and in situ functionalized Dp-Rhi on AuNPs surface was verified by Fourier transform infrared spectroscopy and zeta potentials analysis shows a negative (-18.4mV) surface charges, which confirm that presence of Dp-Rhi on AuNPs. The biocompatibility of Dp-Rhi_AuNPs is also examined by cell viability of FaDu cells using MTS assay and compared to control group. In conclusion, the SERS performance of AuNPs@cellulose paper substrates were systematically demonstrated and examined with different excitation wavelengths (i.e. 532, 632.8 and 785nm lasers) and the as-prepared 3D substrates provided an enhancement factor approaching 7 orders of magnitude compared with conventional Raman intensity using para-nitrothiophenol (p-NTP), para-aminothiophenol (p-ATP) and para-mercaptobenzoic acid (p-MBA) as probe molecules. The strong electromagnetic effect was generated at the interface of AuNPs and pre-treated roughened cellulose paper is also investigated by simulation in which the formation of possible Raman hot-spot zone in fiber-like microstructure of cellulose paper decorated with AuNPs. Notably, with optimized condition of as-prepared 3D AuNPs@cellulose paper is highly sensitive in the SERS detection of aqueous tyrosine (10^-10M) and melamine (10^-9M).

Label-Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches

Raman spectroscopy is an emerging technique in bioanalysis and imaging of biomaterials owing to its unique capability of generating spectroscopic fingerprints. Imaging cells and tissues by Raman microspectroscopy represents a nondestructive and label-free approach. All components of cells or tissues contribute to the Raman signals, giving rise to complex spectral signatures. Resonance Raman scattering and surface-enhanced Raman scattering can be used to enhance the signals and reduce the spectral complexity. Raman-active labels can be introduced to increase specificity and multimodality. In addition, nonlinear coherent Raman scattering methods offer higher sensitivities, which enable the rapid imaging of larger sampling areas. Finally, fiber-based imaging techniques pave the way towards in vivo applications of Raman spectroscopy. This Review summarizes the basic principles behind medical Raman imaging and its progress since 2012.

Raman microscopy at the subcellular level: a study on early apoptosis in endothelial cells induced by Fas ligand and cycloheximide

High spatially resolved Raman microscopy was applied to study the early apoptosis in endothelial cells and chemical and structural changes induced by this process. Application of cluster analysis enabled separation of signals due to various subcellular organelles and compartments such as the nuclei, nucleoli, endoplasmic reticulum or cytoplasm and analysis of alterations locally at the subcellular level. Different stimuli, i.e. Fas ligand, a tumor necrosis factor, and cycloheximide, an inhibitor of eukaryotic protein biosynthesis, were applied to induce apoptotic mechanisms. Due to different mechanisms of action, the changes observed in subcellular structures were different for FasL and cycloheximide. Although in both cases a statistically significant decrease of the protein level was observed in all studied cellular structures, the increase of the nucleic acids content locally in apoptotic nuclei was considerably more pronounced upon FasL-induced apoptosis compared to the cycloheximide one. Additionally, apoptosis invokes also a decrease of the proteins with the α-helix protein structure selectively for FasL in the cytoplasm and endoplasmic reticulum.

Hollow Au nanoflower substrates for identification and discrimination of the differentiation of bone marrow mesenchymal stem cells by surface-enhanced Raman spectroscopy

In this work, a novel surface-enhanced Raman scattering (SERS) substrates based on hollow gold nanoflower (HAuNF)-decorated silicon wafers have been fabricated for detection and identification of the differentiation of bone marrow mesenchymal stem cells.

Plasmon-enhanced fluorescence imaging with silicon-based silver chips for protein and nucleic acid assay

Metal-enhanced fluorescence shows great potential for improving the sensitivity of fluoroscopy, which has been widely used in protein and nucleic acid detection for biosensor and bioassay applications. In comparison with the traditional glass-supported metal nanoparticles (MNPs), the introduction of a silicon substrate has been shown to provide an increased surface-enhanced Raman scattering (SERS) effect due to the coupling between the MNPs and the semiconducting silicon substrate. In this work, we further study the fluorescence-enhanced effect of the silicon-supported silver-island (Ag@Si) plasmonic chips. In particular, we investigate their practical application of improving the traditional immunoassay such as the biotin-streptavidin-based protein assay and the protein-/nucleic acid-labeled cell and tissue samples. The protein assay shows a wavelength-dependent enhancement effect of the Ag@Si chip, with an enhancement factor ranging from 1.2 (at 532 nm) to 57.3 (at 800 nm). Moreover, for the protein- and nucleic acid-labeled cell and tissue samples, the Ag@Si chip provides a fluorescence enhancement factor of 3.0-4.1 (at 800 nm) and a significant improvement in the signal/background ratio for the microscopy images. Such a ready accommodation of the fluorescence-enhanced effect for the immunoassay samples with simple manipulations indicates broad potential for applications of the Ag@Si chip not only in biological studies but also in the clinical field.

Ultrasensitive, Specific, Recyclable, and Reproducible Detection of Lead Ions in Real Systems through a Polyadenine-Assisted, Surface-Enhanced Raman Scattering Silicon Chip

It is of great significance to accurately and reliably detect trace lead(II) (Pb(2+)) ions, preferably at sub-nM level due to the possible long-term accumulation of Pb(2+) in the human body, which may cause serious threats to human health. However, a suitable Pb(2+) sensor meeting the demands is still scanty. Herein, we develop a polyadenine-assisted, surface-enhanced Raman scattering (SERS) silicon chip (0.5 cm × 0.5 cm) composed of core (Ag)-satellite (Au) nanoparticles (Ag-Au NPs)-decorated silicon wafers (Ag-Au NPs@Si) for high-performance Pb(2+) detection. Typically, strong SERS signals could be measured when DNAzyme conjugated on the SERS silicon chip is specifically activated by Pb(2+), cleaving the substrate strand into two free DNA strands. A good linearity exists between the normalized Raman intensities and the logarithmic concentrations of Pb(2+) ranging from 10 pM to 1 μM with a good correlation coefficient, R(2) of 0.997. Remarkably, Pb(2+) ions with a low concentration of 8.9 × 10(-12) M can be readily determined via the SERS silicon chip ascribed to its superior SERS enhancement, much lower than those (∼nM) reported by other SERS sensors. Additionally, the developed chip features good selectivity and recyclability (e.g., ∼11.1% loss of Raman intensity after three cycles). More importantly, the as-prepared chip can be used for accurate and reliable determination of unknown Pb(2+) ions in real systems including lake water, tap water and industrial wastewater, with the RSD value less than 12%.

Combined Labelled and Label-free SERS Probes for Triplex Three-dimensional Cellular Imaging

Cells are complex chemical systems, where the molecular composition at different cellular locations and specific intracellular chemical interactions determine the biological function. An in-situ nondestructive characterization of the complicated chemical processes (like e.g. apoptosis) is the goal of our study. Here, we present the results of simultaneous and three-dimensional imaging of double organelles (nucleus and membrane) in single HeLa cells by means of either labelled or label-free surface-enhanced Raman spectroscopy (SERS). This combination of imaging with and without labels is not possible when using fluorescence microscopy. The SERS technique is used for a stereoscopic description of the intrinsic chemical nature of nuclei and the precise localization of folate (FA) and luteinizing hormone-releasing hormone (LHRH) on the membrane under highly confocal conditions. We also report on the time-dependent changes of cell nuclei as well as membrane receptor proteins during apoptosis analyzed by statistical multivariate methods. The multiplex three-dimensional SERS imaging technique allows for both temporal (real time) and spatial (multiple organelles and molecules in three-dimensional space) live-cell imaging and therefore provides a new and attractive 2D/3D tracing method in biomedicine on subcellular level.

Oligonucleotide-based biosensors for in vitro diagnostics and environmental hazard detection

Oligonucleotide-based biosensors have drawn much attention because of their broad applications in in vitro diagnostics and environmental hazard detection. They are particularly of interest to many researchers because of their high specificity as well as excellent sensitivity. Recently, oligonucleotide-based biosensors have been used to achieve not only genetic detection of targets but also the detection of small molecules, peptides, and proteins. This has further broadened the applications of these sensors in the medical and health care industry. In this review, we highlight various examples of oligonucleotide-based biosensors for the detection of diseases, drugs, and environmentally hazardous chemicals. Each example is provided with detailed schematics of the detection mechanism in addition to the supporting experimental results. Furthermore, future perspectives and new challenges in oligonucleotide-based biosensors are discussed.

Highly sensitive and reproducible silicon-based surface-enhanced Raman scattering sensors for real applications

During the past few decades, thanks to silicon nanomaterials’ outstanding properties, different dimensional silicon nanostructures have been employed for designing and fabricating high-performance surface-enhanced Raman scattering (SERS) sensors for chemical and biological detection.

Early apoptosis real-time detection by label-free SERS based on externalized phosphatidylserine

Early apoptosis real-time detection by label-free SERS based on externalized phosphatidylserine usingin situsynthesized silver nanoparticles.

Isothermal Amplification of Nucleic Acids

Isothermal amplification of nucleic acids is a simple process that rapidly and efficiently accumulates nucleic acid sequences at constant temperature. Since the early 1990s, various isothermal amplification techniques have been developed as alternatives to polymerase chain reaction (PCR). These isothermal amplification methods have been used for biosensing targets such as DNA, RNA, cells, proteins, small molecules, and ions. The applications of these techniques for in situ or intracellular bioimaging and sequencing have been amply demonstrated. Amplicons produced by isothermal amplification methods have also been utilized to construct versatile nucleic acid nanomaterials for promising applications in biomedicine, bioimaging, and biosensing. The integration of isothermal amplification into microsystems or portable devices improves nucleic acid-based on-site assays and confers high sensitivity. Single-cell and single-molecule analyses have also been implemented based on integrated microfluidic systems. In this review, we provide a comprehensive overview of the isothermal amplification of nucleic acids encompassing work published in the past two decades. First, different isothermal amplification techniques are classified into three types based on reaction kinetics. Then, we summarize the applications of isothermal amplification in bioanalysis, diagnostics, nanotechnology, materials science, and device integration. Finally, several challenges and perspectives in the field are discussed.

Silicon nanostructures for cancer diagnosis and therapy

The emergence of nanotechnology suggests new and exciting opportunities for early diagnosis and therapy of cancer. During the recent years, silicon-based nanomaterials featuring unique properties have received great attention, showing high promise for myriad biological and biomedical applications. In this review, we will particularly summarize latest representative achievements on the development of silicon nanostructures as a powerful platform for cancer early diagnosis and therapy. First, we introduce the silicon nanomaterial-based biosensors for detecting cancer markers (e.g., proteins, tumor-suppressor genes and telomerase activity, among others) with high sensitivity and selectivity under molecular level. Then, we summarize in vitro and in vivo applications of silicon nanostructures as efficient nanoagents for cancer therapy. Finally, we discuss the future perspective of silicon nanostructures for cancer diagnosis and therapy.

Thickness of a metallic film, in addition to its roughness, plays a significant role in SERS activity

In this paper we evaluate the effect of roughness and thickness of silver film substrates, fabricated on glass and polydimethylsiloxane (PDMS) templates, on surface-enhanced Raman Spectroscopy (SERS) activity. While the silver substrates obtained on glass templates exhibit nm-scale roughness, the silver substrates on PDMS templates show larger roughness, on the order of 10 s of nm. These roughness values do not change significantly with the thickness of the silver film. The SERS intensities of 4-aminothiophenol (ATP) deposited on these substrates strongly depend on both roughness and thickness, with more significant contribution from the roughness on thinner films. FEM simulations of the electric field intensities on surfaces of different thicknesses for rough and flat surfaces suggest higher localized plamons on thinner, rough surfaces. This study indicates that, besides roughness, the thickness of the metallic layer plays a significant role in the SERS activity.

Label-Free in Situ Discrimination of Live and Dead Bacteria by Surface-Enhanced Raman Scattering

Techniques to distinguish between live and dead bacteria in a quantitative manner are in high demand in numerous fields including medical care, food safety, and public security as well as basic science research. This work demonstrates new nanostructures (silver nanoparticles coating bacteria structure, Bacteria@AgNPs) and their utility for rapid counting of live and dead bacteria by surface-enhanced Raman scattering (SERS). We found that suspensions containing Gram-negative organisms as well as AgNPs give strong SERS signals of live bacteria when generated selectively on the particle surface. However, almost no SERS signals can be detected from Bacteria@AgNPs suspensions containing dead bacteria. We demonstrate successful quantification of different percentages of dead bacteria both in bulk liquid and on glass surfaces by using SERS mapping on a single cell basis. Furthermore, different chemicals have been used to elucidate the mechanism involved in this observation. Finally, we used the Bacteria@AgNPs method to detect antibiotic resistance of E. coli strains against several antibiotics used in human medicine.

Applying fluorescence lifetime imaging microscopy to evaluate the efficacy of anticancer drugs

Fluorescence lifetime imaging microscopy was applied to evaluate the efficacy of anticancer drugs. A decrease in the fluorescence lifetime of the nucleus in apoptotic cancer cells stained by SYTO 13 dye was detected after treatment with antitumor antibiotics such as doxorubicin or epirubicin. It was confirmed that the change in fluorescence lifetime occurred earlier than morphological changes in the cells. We found that the fluorescence lifetime of the nucleus in the cells treated with epirubicin decreased more rapidly than that of the cells treated with doxorubicin. This implies that epirubicin was more efficacious than doxorubicin in the treatment of cancer cells. The change in fluorescence lifetime was, however, not indicated when the cells were treated with cyclophosphamide. The decrease in fluorescence lifetime was associated with the processes involving caspase activation and chromatin condensation. Therefore, this technique would provide useful information about apoptotic cells, particularly in the early stages.