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A highly sensitive nanoscale mass sensor was developed for weight measurement of single microparticle using suspended graphene structure. The sensor is composed of an array of holes covered with suspended monolayer graphene. Based on the shift of 2D Raman peak in graphene, originated from elongation of carbon-carbon bonds under pressure, the mass of microparticle on suspended graphene can be measured. The results show the sensor can detect microparticle with mass range from 0.1 ng to 3 ng. The peak shift ratio is -69.8 cm-1 per 1% strain for experiment value and -72.3 cm-1 per 1% strain for calculated value. The demonstrated concept presents a promising path for nano-mass measurement applications.

One-dimensional and two-dimensional materials are widely used to compose the conductive network atop soft substrate to form flexible strain sensors for several wearable electronic applications. However, limited contact area and layer misplacement hinder the rapid development of flexible strain sensors based on 1D or 2D materials. To overcome these drawbacks above, we proposed a hybrid strategy by combining 1D carbon nanotubes (CNTs) and 2D graphene nanoplatelets (GNPs), and the developed strain sensor based on CNT-GNP hierarchical networks showed remarkable sensitivity and tenability. The strain sensor can be stretched in excess of 50% of its original length, showing high sensitivity (gauge factor 197 at 10% strain) and tenability (recoverable after 50% strain) due to the enhanced resistive behavior upon stretching. Moreover, the GNP-CNT hybrid thin film shows highly reproducible response for more than 1000 loading cycles, exhibiting long-term durability, which could be attributed to the GNPs conductive networks significantly strengthened by the hybridization with CNTs. Human activities such as finger bending and throat swallowing were monitored by the GNP-CNT thin film strain sensor, indicating that the stretchable sensor could lead to promising applications in wearable devices for human motion monitoring.

Tunability of facilitation in short-term memory (STM) provides great potential in bioinspired computing. Recently, several doping strategies were proposed to modify the intrinsic features of materials, resulting in the optimization of the facilitation index (FI). However, real-time scale tuning, which is implemented on the same synaptic device, has not yet been demonstrated. Inspired by the chemical-electrical mixed synapse structure in the brain, we propose a three-terminal artificial synapse based on an ion-gated MoS2 memristor. The gate terminal serves as a nonvolatile ionic pump via chemical intercalation, which effectively affects both the conductance baseline and the hysteresis degree of the STM effect of the memristor. We further modeled the postsynaptic current (PSC) behavior and used it for reservoir computing. Simulation results show that, due to the real-time tuning ability, the built reservoir can be programmed for specific handwritten recognition tasks with the pruning of neurons from 784 to 50. The developed artificial mixed synapse is promising for a downsampling module in neural network design.

The detection of carbohydrates in human body fluids is critical for disease diagnosis and healthy monitoring. Despite recent advances in glucose sensing, multiplex detection of different carbohydrates within a single assay that is capable of efficiently providing richer health information remains challenging. Herein, we report a versatile surface-enhanced Raman spectroscopy-based platform for the quantitative detection of monosaccharides (glucose, fructose, and galactose) in one test using a displace-and-trap mechanism. Moreover, due to the use of multiple optical interference-free (1800-2200 cm-1) signal-independent Raman probes, the detection range of this platform (0.125-7 mg/dL) perfectly covers physiological concentrations, enabling the quantitative detection of glucose and galactose in clinical human saliva samples. This work provides a noninvasive and high-efficiency potential tool for the screening of clinical diabetes and other carbohydrate-related diseases.

We report a broadband photodetector based on vertically stage-liked MoS2/Si heterostructure with MoS2 sheet modified using rapid annealing technique. The fabricated photodetector features a unique structure of naturally formed band alignment in MoS2 after annealing and shows an ultra-high responsivity up to 746 mA W−1 and detectivity up to 6.03 × 1011 Jones ranging from 405 to 980 nm, as well exhibits a fast response speed with a rise time of ∼178 µs and fall time of ∼198 µs. The demonstrated superb photodetector suggests an effective way to form vertical p-n junction for improving the performances of future optoelectronic devices.

Recent advances in surface-enhanced Raman scattering (SERS) have offered great promise for the early-stage diagnosis of life-threatening diseases by in vivo sensing and imaging techniques as well as a treatment and evaluation of its efficacy. The SERS technique makes use of specially designed tags made up of a metallic nanoparticle, a Raman reporter molecule, a biocompatible protection layer, and a sensing layer, realizing the signal amplification by the electromagnetic enhancement (EE) originating from the plasmon excitation of metal nanostructures and chemical enhancement (CE) owing to chemical interactions and photon-induced charge transfer between the metal and target molecule. These SERS tags have been proven to be a promising candidate for medical applications compared to other conventional techniques because of their high sensitivity, low detection limit, good selectivity, high photostability, low interferences from biological matrices, and multiplexing capabilities. As a result, there has been a surge in the reports for developing SERS tags for molecular diagnostics, immunoassays, biomarker detection, and drug screening applications. Here, we review the recent progress made in the development of SERS tags, including the preparation strategies and properties of SERS tags. The multiple uses of SERS tags in the detection of biomarkers, proteins, cancer and stem cells, cell labeling drug delivery, photothermal therapy, and multimodal imaging techniques have also been reviewed and discussed. Finally, we provide a forward look at how SERS tags may overcome their limitations to guide future SERS tags design with clinical outcomes. This work was supported by the University of Sydney (Startup Grant, Australia) and the National Natural Science Foundation of China (21975005, China).

The limited availability of nasopharyngeal carcinoma-related progression biomarker array kits that offer physicians comprehensive information is disadvantageous for monitoring cancer progression. To develop a biomarker array kit, systematic identification and differentiation of a large number of distinct molecular surface-enhanced Raman scattering (SERS) reporters with high spectral temporal resolution is a major challenge. To address this unmet need, we use the chemistry of metal carbonyls to construct a series of unique SERS reporters with the potential to provide logical and highly multiplex information during testing. In this study, we report that geometric control over metal carbonyls on nanotags can produce 14 distinct barcodes that can be decoded unambiguously using commercial Raman spectroscopy. These metal carbonyl nanobarcodes are tested on human blood samples and show strong sensitivity (0.07 ng/mL limit of detection, average CV of 6.1% and >92% degree of recovery) and multiplexing capabilities for MMPs., SERS assays have potential for multiplexed detection of biomarkers but differentiation of SERS tags remains a challenge. Here, the authors report the creation of 14 distinct geometrically controlled metal carbonyl tags and demonstrate multiplexed detection of nasopharyngeal carcinoma biomarkers from patient blood.

Two-dimensional layered molybdenum disulfide (MoS2) exhibits great potential for applications in optoelectronic devices, especially photodetectors. However, most of the reported MoS2-based photodetectors only show limited absorption in visible range, resulting in narrow spectral response with poor sensitivity. Integrating plasmonic nanoparticles with MoS2 provides a promising approach to enhance light-matter interactions and detector responsibility. We here report a plasmon-enhanced photodetector based on Au/MoS2 heterostructure with Au nanoparticles (NPs) deposited on the surface of few-layer MoS2 by magnetron sputtering. By coupling with Au NPs, the interactions between ultra-thin MoS2 and incident lights are greatly enhanced via localized surface plasmon resonance. With this new architecture, the spectral response of few-layer MoS2 based photodetector is extended to near-infrared region (700–1600 nm). Further, measurements show that significant improvement of photocurrent is observed with the highest value reaching up to 64 mAW−1 at incident wavelength of 980 nm. With the demonstrated superb performance the proposed detector represents a viable path towards implementing ultra-sensitive near-infrared detection.

The diode-triggered silicon-controlled rectifier (DTSCR) is an important device for the electrostatic discharge (ESD) protection of low-voltage integrated circuits, and its trigger voltage is determined by the forward turn-on voltage of diode string and the voltage drops on the parasitic resistors of metal interconnects. For the conventional DTSCR, the voltage drops on the parasitic resistors are often negligible so its triggering voltage is mainly determined by the forward turn-on voltage of diode string, which decreases with increasing temperature due to the inherited negative temperature coefficient. In this paper, an improved and novel device called thermal-stable DTSCR (TSDTSCR) is proposed to offer an improved ESD protection stability at elevated temperatures. This is done by changing and optimizing the 3-D layout. In particular, the experimental results show that the trigger voltage drop of the TSDTSCR can be reduced to 13.5% at 125 °C, comparing to 27.18% of the DTSCR. The holding voltage of the TSDTSCR is also more stable than that of the DTSCR over a wide range of temperatures.

A dual signal amplification method based on surface-enhanced Raman scattering (SERS) is developed by photo-triggered release of SERS probes from mesoporous silica-coated Au nanorods (SiO2@Au) and the use of a specially-designed SERS substrate with an internal reference. Two metal carbonyl (metal-CO) labels (Os-SCO and Re-SCO) are proposed here as novel interference-free labels. Results demonstrate that tumor-related DNA can be quantitatively detected by this reliable and ultra-sensitive SERS platform.

Resistive switching (RS) can be divided into two categories, namely nonvolatile memory switching and volatile threshold switching, depending on the volatility. MoO3 is one type of versatile transition metal oxide with a high work function, large electron affinity and wide band gap for potential applications in electronics, optoelectronics, batteries and electrochromic devices. Herein, we report the transition from nonvolatile memory to volatile threshold switching in single MoO3 nanobelts simply by changing the electrodes from Au to Ag. The one-dimensional (1D) α-MoO3 nanobelts are synthesized by a hydrothermal method and annealed under different atmospheres to adjust the concentration of oxygen vacancies. The prepared single MoO3 nanobelt is used to serve as the RS layer to construct lateral two-terminal RS devices. By using Au as the electrodes, the MoO3 nanobelts exhibit typical nonvolatile bipolar memory RS behaviors. On the other hand, bidirectional threshold RS properties can be achieved by employing Ag as the electrodes due to the large contact resistance between Ag and MoO3. More importantly, the threshold RS performance is significantly enhanced by annealing the nanobelts in N2. The ON/OFF current ratio is increased up to 3 × 105 while the threshold voltage is decreased down to 0.75 V. These results demonstrate the diverse RS behaviors in single 1D MoO3 nanobelts and potential applications in volatile and non-volatile switching devices. In addition, the finding provides guidelines for improvement and/or alternation of RS behaviors through defect engineering and/or device modification in the multifunctional emerging devices.

We propose an anti-scratch flexible surface-enhanced Raman scattering substrate with arrayed nanocavity microstructures fabricated by colloidal lithography. The nanocavity microstructure of the substrate can well protect the inner gold nanoparticles during wipe sampling. The prepared flexible substrate was able to detect 4-aminothiophenol (4-ATP) with a concentration down to 1 fM. Furthermore, the substrate was used to detect 6-BA residues on the surface of apples and bean sprouts through wipe sampling, which shows great potential in the field of rapid on-site detection, especially in the detection of pesticide residues on the surface of fruits and vegetables.

A nanoscale photodetector is a crucial part of intelligent imaging and wireless communication devices. Building van der Waals (vdWs) heterostructures based on two-dimensional transition metal dichalcogenides is thought to be a smart approach for achieving nanoscale photodetectors. However, the pinning effect induced by surface states, defects, and metal-induced gap states during the fabrication process of vdWs heterostructures and contacting electrodes leads to a large Schottky barrier and consequently limits the photoresponse of vdWs heterostructures. In this study, a photodetector based on the WSe2/MoS2 heterostructure with graphene (Gr)/indium tin oxide (ITO) hybrid electrodes has been fabricated. The vdWs contacts established between the exfoliated graphene layers and WSe2/MoS2 heterostructure are able to get rid of lattice damages caused by atom bombardment during the deposition of metal electrodes. In addition, the reduced Schottky barrier at graphene/heterostructure interfaces facilitates the transport of carriers. Experimental results show that the photodetector based on WSe2/MoS2 heterostructures with Gr/ITO hybrid electrodes exhibits a high responsivity of up to 1236.5 A W−1, a detectivity of up to 1.23 × 1013 Jones, and a fast response of 270/130 μs to light from the ultraviolet to near-infrared range.

A highly responsive, flexible piezoresistive strain sensor was demonstrated using laser thermal reduced graphene oxide doped with polystyrene nanoparticles. The nanoparticles alter the morphology of the sensing film by separating stacked graphene fragments and creating partially connected conducting channels, which significantly increase the resistance change under strain. Two types of distinctive resistance-changing mechanisms were observed associated with doping of nanoparticles with different sizes. Compared with graphene oxide based strain sensors, the measured gauge factor of the sensor doped with 90 nm nanoparticles can reach up to 250 under small deformation (linear region below 1.05%). Furthermore, the flexible strain sensor was applied for real-time monitoring of human body activities including swallowing process, lower back posture and pulse on neck. The demonstrated results present the potential of a viable sensing material for a number of human health monitoring applications in preventing injuries and detecting certain disease-related disorders.

Optoplasmonic materials comprising both photonic and plasmonic elements are of particular interest for the development of substrates for surface-enhanced Raman spectroscopy (SERS). In this work, a layer of analyte-carrying dielectric nano/microspheres is placed on top of a monolayer of gold nanoparticles to enhance the intensity of the electric (E-) field localization and to enrich the analyte close to the electromagnetic hot spots. Numerical simulations of the hybrid structure confirm an increased and spatially expanded E-field enhancement at the interface. Due to a decreasing filling fraction with increasing size of the dielectric spheres, simulations predict a saturated SERS enhancement for dielectric microspheres with a diameter larger than 4 μm, which is confirmed by experimental SERS measurements. The dielectric microsphere can be functionalized with surface ligands that facilitate the binding of target molecules in solution. The deposition of the analyte-loaded microspheres on the self-assembled gold nanoparticle ensures a high local concentration of analytes in the electromagnetic "hot" surface. The performance of the optoplasmonic SERS approach for detecting methamphetamine in saliva and urine is tested, and the detection of analytes at nanomolar (nM) concentrations is demonstrated.

Three-dimensional (3D) surface enhanced Raman scattering (SERS) substrates were produced by magnetic force assisting self-assembled nanoparticles in arrayed holes. Compared to '2D' plasmonic structures used in conventional SERS substrates, the 'hot spots' existed on whole depth of the 3D SERS substrates, which greatly enhanced the sensitivity. The prepared 3D SERS substrate was able to detect 4-aminothiophenol with a concentration down to 1 pM. Furthermore, the substrate was applied to detect hexachlorobenzene residue in soil, indicating its great potential for rapid and sensitive detection of extreme low concentrated molecules, especially pollutants residues in foods and environments.

By taking advantage of the spectral properties of metal carbonyls, we have designed a surface-enhanced Raman spectroscopy (SERS) ratiometric assay for measuring cell-free circulating DNA (cfDNA) from Epstein-Barr virus in blood for nasopharyngeal carcinoma (NPC). This assay consists of a rhenium carbonyl (Re–CO) to serve as a DNA probe, an osmium carbonyl (Os–CO) embedded within the SERS-active substrate as an internal reference, and a streptavidin layer on the surface of the substrate. Hybridization of cfDNA with biotinylated-capture sequence leads to immobilization of cfDNA on the substrate. The binding of Re–CO via daunorubicin (DNR) to cfDNA is accompanied by an appearance of a strong symmetry stretching vibrations peak at 2113 cm–1, which has spectral overlap with Os–CO (2025 cm–1). This results in an increase in the I2113/I2025 ratio and quantitatively correlates with cfDNA. This SERS assay can be readily used to detect cfDNA in blood samples from patients due to the intensity ratio of I2113/I2025 l...

As an essential part of the Internet of Things (IoT), the identification technology is expected to meet higher requirements in terms of safety and durability due to the rapid development of the IoT, and signal recognition-based smart identification technologies that are highly secure, reliable, and even self-powered have attracted considerable attention in recent years. Herein, we present a self-powered double-authentication microsystem (DAM) composed of a piezoelectric-based active code and a triboelectric-based self-driven code to realize a high-security, high-identification-rate, and self-powered smart identification system. Polyvinylidene fluoride (PVDF) films with different lengths were arranged in binary sequence to construct the piezoelectric-based active code. A complementary filler and an opaque cover were implemented to conceal the coded information. The high consistency of output amplitudes of length-consistent piezoelectric units, the great difference of output amplitudes of length-inconsistent piezoelectric units, and the ultra-small speed dependence were experimentally confirmed, which enable the piezoelectric-based active code to achieve a high identification accuracy rate. The triboelectric-based self-driven code was implemented by a relative-sliding mode triboelectric nanogenerator (RS-TENG) to drive an information storage unit, such as a pre-compiled liquid crystal display (LCD). The obtained electrical energy during one operation could drive the LCD for ~26 s, which allows the operator to have enough time to read the information. In addition, as attractive application prototypes, the two coded information were combined to realize personal identification and automatic unlocking. The high safety and identification accuracy rate make the self-powered DAM have attractive feasibility for applications in smart identification field.

This work presents a highly sensitive flexible tactile sensor based on microstructured multi-wall carbon nanotube (MWCNT) arrays with patterned cross-contacted electrodes. The anisotropic microstructures not only empower the sensor with an ultra-high sensitivity of − 9.95 kPa− 1 at low pressure level below 100 Pa, about 100 times higher than that of an unstructured sensor, but also lead to great stability and a fast response time (

Graphene has been demonstrated as a candidate for optoelectronic devices due to its broad absorption spectrum and ultra-high carrier mobility. However, graphene is essentially transparent in visible and near-infrared regimes with an absorptivity of 2.3%, which largely limits its application in photodetection. Here, we show that metallic nanopillar antennas could improve light absorption in graphene detectors. The coupled antennas help to concentrate a free space electromagnetic wave around the nanopillars by localized surface plasmon resonance, strongly impacted by geometrical design. It is found that spectral selectivity can be realized by tuning key geometrical parameters such as period, radius, and height of the metallic nanopillar, leading to wavelength-tunable photodetectors within a broad range from 0.6 μm to 1.2 μm. With the optimized design, the detector exhibits an excellent photoresponsivity of 7 A W-1 at a wavelength of 0.82 μm.

Surface-enhanced Raman spectroscopy (SERS) is garnering considerable attention for the swift diagnosis of pathogens and abnormal biological status, that is, cancers. In this work, a simple, fast and inexpensive optical sensing platform is developed by the design of SERS sampling and data analysis. The pretreatment of spectral measurement employed gold nanoparticle colloid mixing with the serum from patients with colorectal cancer (CRC). The droplet of particle-serum mixture formed coffee-ring-like region at the rim, providing strong and stable SERS profiles. The obtained spectra from cancer patients and healthy volunteers were analyzed by unsupervised principal component analysis (PCA) and supervised machine learning model, such as support-vector machine (SVM), respectively. The results demonstrate that the SVM model provides the superior performance in the classification of CRC diagnosis compared with PCA. In addition, the values of carcinoembryonic antigen from the blood samples were compiled with the corresponding SERS spectra for SVM calculation, yielding improved prediction results.

We demonstrate a tunable longwave infrared photodetector with ultra-high sensitivity based on graphene surface plasmon polaritons controlled by ferroelectric domains. The simulated results show that the photodetector shows a tunable absorption peak, modulated by periodically polarized ferroelectric domains at the nanoscale, with an ultra-high responsivity up to 7.62 × 106 A W-1 and a detectivity of ∼6.24 × 1013 Jones (Jones = cm Hz1/2 W-1) in the wavelengths ranging from 5 to 20 μm at room temperature. The potential mechanism for the prominent performances of the proposed photodetector can be attributed to the highly confined graphene surface plasmons excited by the local electrical field across the interface of the graphene and ferroelectric layer resonant to the incident wavelength, which could be easily controlled by the features of the ferroelectric domains. Compared with the silicon-based graphene plasmonic photodetector using a complex process of micro-nano fabrication, the proposed photodetector provides the advantages of a more convenient and controllable technique without the need for patterning graphene, and lower energy consumption due to the non-volatile properties of the ferroelectrics without an additional contact electrode. The tunable spectral response and the ultra-high responsivity make the graphene plasmonic photodetector tuned by the ferroelectric domains promising in practical applications of micro-spectrometers and other light sensing devices.

We demonstrated a polarization-sensitive photodetector based on periodically crossed graphene ribbons theoretically. Localized surface plasmon is generated by patterned graphene structure with significantly enhanced incident light absorption. Broadband detection is observed from 10.5 to 16.5 μm. Moreover, the photoresponsivity reaches up to 1.717 A W-1 at the wavelength of 12.58 μm under 0° polarization, and the photoresponsivity is 0.212 A W-1 under 90° polarization. The tunability of photodetectors is achieved by changing the gate voltage to modulate the chemical potential of graphene. The finite difference time domain solutions are used to predict the performance of the photodetector with different polarization angles for longwave infrared (LWIR) light. The polarization-sensitive, tunable and broadband graphene photodetector provides a promising direction for high performance LWIR detection at room temperature.

We demonstrate an ultra-sensitive photodetector based on a graphene/monolayer MoS2 vertical heterostructure working at room temperature. Highly confined plasmon waves are efficiently excited through a periodic array of monolayer graphene ribbons in which plasmon resonance has remarkably large oscillator strength, resulting in a sharp optical absorption peak in the normal-incidence transmission spectrum. A significant amount of electron–hole pairs are produced in graphene ribbons by optical absorption, separated by the built-in electric field across the graphene/MoS2 heterojunction. The responsivity reaches up to 1 × 107 A W−1 at room temperature due to very strong resonance in the heterostructure, yielding a highly sensitive graphene-based photodetector. Additionally, the absorption can be tuned over a wide spectral range (6–16 μm) by varying gate biasing. The ultra-sensitive, spectrally tunable photodetector could be potentially used as a promising candidate for mid-infrared micro-spectrometers.

A flexible 4 × 4 sensor array with 16 micro-scale capacitive units has been demonstrated based on flexible piezoelectric poly(vinylidene fluoride) (PVDF) film. The piezoelectricity and surface morphology of the PVDF were examined by optical imaging and piezoresponse force microscopy (PFM). The PFM shows phase contrast, indicating clear interface between the PVDF and electrode. The electro-mechanical properties show that the sensor exhibits excellent output response and an ultra-high signal-to-noise ratio. The output voltage and the applied pressure possess linear relationship with a slope of 12 mV/kPa. The hold-and-release output characteristics recover in less than 2.5 μs, demonstrating outstanding electro-mechanical response. Additionally, signal interference between the adjacent arrays has been investigated via theoretical simulation. The results show the interference reduces with decreasing pressure at a rate of 0.028 mV/kPa, highly scalable with electrode size and becoming insignificant for pressure level under 178 kPa.

Matrix metalloproteinases (MMPs), specifically MMP-2, MMP-7, and MMP-9, have been discovered to be linked to many forms of vascular diseases such as stroke, and their detection is crucial to facilitate clinical diagnosis. In this work, we prepared a class of optical interference-free SERS nanotags (CO-nanotags) that can be used for the purpose of multiplex sensing of different MMPs. Multiplex detection with the absence of cross-talk was achieved by using CO-nanotags with individual tunable intrinsic Raman shifts of CO in the 1800–2200 cm–1 region determined by the metal core and ligands of the metal carbonyl complex. Boolean logic was used as well to simultaneously probe for two proteolytic inputs. Such nanotags offer the advantages of convenient detection of target nanotags and high sensitivity as validated in the ischemia rat model.

In this work, we propose a novel glucose binding mechanism on a highly sensitive SERS substrate, in order to overcome challenges in specific glucose detection in bio-fluids. We make use of phenylboronic acid as a receptor for saccharide capture onto the substrate and the ability of the captured glucose molecule to undergo secondary binding with an alkyne-functionalized boronic acid to form a glucose-alkyne-boronic acid complex. The formation of this complex shows high selectivity for glucose, over other saccharides. In addition, the alkyne group of the alkyne-functionalized boronic acid exhibits a distinct Raman peak at 1996 cm(-1) in a biological silent region (1800-2800 cm(-1)) where most endogenous molecules, including glucose, show no Raman scattering, thus offering a high sensitivity over other SERS glucose sensing. The substrate offers long-term stability, as well as high SERS enhancement to the glucose-alkyne boronic acid complex on substrate. In addition, the reversibility of SERS signals at various incubation stages also shows reusability capabilities, whereas positive results in clinical urine samples demonstrate clinical feasibility. All these strongly suggest that this newly developed SERS-based assay offers great potential in glucose sensing.

Coexistence of non-volatile and volatile resistive switching on the same device are of interest in memory devices for weight storage applications. In this work, stacked MoS2 nanosheet thin film was modified using soft nitrogen plasma treatment (NPT). Compared to pristine MoS2-based counterparts, the fabricated Ag/NPT-MoS2/indium tin oxide (ITO) structure exhibited both an enhanced ratio of 104 and lowered threshold voltage of 0.1 V. The distinction might be attributed to the introduced carbonitride between Ag and MoS2, where the conductive filaments and interface barrier altogether affect the switching. The observation suggested a possibility of programming on a single two-terminal device.

Laser heating provides an effective method to produce thermally reduced graphene oxide (rGO), it can also pattern the designed layout on the surface of graphene oxide (GO) during the reduction process. In this work, we demonstrated a flexible strain sensor based on the morphologically modulated laser-patterned reduced graphene oxide (LPG) film with a one-step process. Compared with the strain sensor using flat patterned rGO (0-1.2%) and curved-grid patterned rGO (CGPG) (0-4.1%), the strain sensor based on rectangular-grid patterned rGO (RGPG) have highest gauge factor (GF), up to 133 under 2.7% of physical deformation. Meanwhile, the RGPG strain sensors exhibit extraordinary linearity in a relatively large range of deformation (0-2.7%) and excellent endurance for over 1000 stretching-releasing circles. The RGPG strain sensor was used to monitor human fatigue. By analyzing eye blinking frequency and duration, it is possible to evaluate the fatigue level. We anticipate that the RGPG based strain sensor, prepared via a relatively simple and cost-effective process, may open up a broad spectrum of practical applications, such as driver fatigue evaluation and smart monitoring of human body movements.

Gold nanorods (GNR) are synthesized using cetylmethylammonium bromide (CTAB) surfactants which function as structure-directing agents. However, CTAB forms a tightly bound cationic bilayer on GNR surface with the cationic trimethylammonium head group exposed to the aqueous media, which is known to be highly toxic in vitro and in vivo. Pluronic is a non-ionic triblock polymer, which can associate with CTAB and form stable CTAB–polymer complexes due to hydrophobic interactions. In this work, two types of Pluronic triblock copolymers were used to encapsulate GNR to reduce their cytotoxicity and improve colloidal and optical stability for biological applications. These formulations were characterized by UV–vis absorption spectra analysis, transmission electron microscopy, cell viability studies, differential interference contrast microscopy and dark-field imaging.

We investigate the dispersion property of space filling mode of photonic crystal structures and find a new type of dispersion—structure induced dispersion. By incorporating this new source of dispersion we designed PCF with large normal dispersion ~ 350 ps 2 /km. Our simulation indicates the dispersion of such fiber changes less than 3% in 1.4–1.7 μm wavelength range and we also show that our design is insensitive to the structure changes.

International audience; We demonstrate a side-channel photonic crystal fiber for surface enhanced Raman scattering applications. A low detection concentration of 5 pM 4-aminothiophenol solution and an accumulative effect of Raman signal along the fiber length are achieved.

International audience; An ultrasensitive surface enhanced Raman spectroscopy (SERS) based sensing platform was developed to detect the mean sialic acid level on the surface of single cell with sensitivity as low as 2 fmol. This platform adopted the use of an interference-free Raman tag, 4-(dihydroxyborophenyl) acetylene (DBA), which selectively binds to sialic acid on the cell membrane. By loading the side channel of a photonic crystal fiber with a mixture of gold nanoparticles and DBA-tagged HeLa cell, and subsequently propagating laser light through the central solid core, strong SERS signal was obtained. This SERS technique achieved accurate detection and quantification of concentration of sialic acid on a single cell, surpassing previously reported methods that required more than 105 cells. Moreover, this platform can be developed into a clinical diagnostic tool to potentially analyze sialic acid-related diseases such as tumor malignancy and metastasis in real-time.

SERS enhancement factor (EF) of planar substrates depends on the size and shape of the fine nanostructure forming a defect free, well-arranged matrix. Nano-lithographic process is considered to be the most advanced methods employed for the fabrication SERS substrates. Nanostructured plasmonic substrates with nanogap (NG) pattern often results in stable, efficient and reproducible SERS enhancement. For such substrates, NG and their diagonal length (DL) need to be optimized. Theoretically smaller NGs (∼30-40 nm or smaller) results in higher SERS enhancement. However, fabrication of NG substrates below such limit is a challenge even for the most advanced lithography process. In this context, herein, we report the optimization of fabrication process, where higher SERS enhancement can be realized from larger NGs substrates by optimizing their DL of nanostructures between the NGs. Based on simulation we could demonstrate that, by optimizing the DL, SERS enhancement from larger NG substrate such as 60 and 80 nm could be comparable to that of smaller (40nm) NG substrates. We envision that this concept will open up new regime in the nanofabrication of practically feasible NG based plasmonic substrates with higher SERS enhancement. Initial results of our experiments are in close agreement with our simulated study.

An optical fiber twist sensor is proposed by using solid core low birefringence photonic crystal fiber (LB-PCF)-based Sagnac interferometer. The twist effects on the fiber are theoretically analyzed. The results show that the dip wavelength of the transmission spectrum shifts with the twist angle with a high sensitivity and resolution of 1.00 nm/0 and 0.010 , respectively. The sensor is also insensitive to environmental temperature change with an ultralow thermal dependent coeffiecient of -0.5 pm/0C.

In this work, we investigated the cytotoxicity, colloidal stability and optical property of gold nanorods before and after functionalizing them with thiolated PEG and Pluronic triblock copolymer (PEO–PPO–PEO) molecules. The morphology of functionalized gold nanorods was characterized by UV–visible absorption spectroscopy, transmission electron microscopy, and dynamic light scattering. Solution phase synthesis of gold nanorods has remained the method of choice for obtaining varying shapes and aspect ratios of rod nanoparticles. This method typically involves the use of cetyltrimethylammonium bromide (CTAB) surfactants as directing agents to grow gold nanorods in the solution phase. The as-synthesized gold nanorods surfaces are terminated with CTAB molecules and this formulation gives rise to adverse toxicity in vitro and in vivo. To employ the gold nanorods for biological studies, it is important to eliminate or minimize the exposure of CTAB molecules from the gold nanorods surface to the local environment such as cells or tissues. Complete removal of CTAB molecules from the gold nanorods surface is unfeasible as this will render the gold nanorods structurally unstable, causing the aggregation of particles. Here, we investigate the individual use of thiolated PEG and PEO–PPO–PEO as capping agents to reduce the cytotoxicity of gold nanorods formulation, while maintaining the optical, colloidal, and structural properties of gold nanorods. We found that encapsulating gold nanorods with the thiolated PEG or PEO–PPO–PEO molecules guarantees the stability and biocompatibility of the nanoformulation. However, excessive use of these molecules during the passivation process leads to a reduction in the overall cell viability. We also demonstrate the use of the functionalized gold nanorods as scattering probes for dark-field imaging of cancer cells thereby demonstrating their biocompatibility. Our results offer a unique solution for the future development of safe scattering color probes for clinical applications such as the long term imaging of cells and tissues. Published version

A metal carbonyl-functionalized nanostructured substrate can be used in a rapid and simple assay for the detection of A1AT, a potential biomarker for bladder cancer, in clinical urine samples. The assay involves monitoring changes in the carbonyl stretching vibrations of the metal carbonyl via surface-enhanced Raman spectroscopy (SERS). These vibrations lie in the absorption spectral window of 1800–2200 cm−1, which is free of any spectral interference from biomolecules. ASTAR (Agency for Sci., Tech. and Research, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore)

In this contribution, we show that Au NRs functionalized with PEG molecules can be used as absorption nanoprobes for near-infrared imaging in live animals. We have found that the contrast signal of the in vivo image is dependent upon the transmission ability of the NIR light interacting with the different aspect ratios of Au NRs. Our study was focused on absorption in vivo imaging at 700 nm, which is within the transmission window of the skin. NIR absorption in vivo imaging was carried out by subcutaneous injection of mice with PEGylated Au NRs that have a LSPR around 700 nm. The formulation showed strong contrast signals under the tissues upon irradiation with NIR light. More importantly, our theoretical calculation suggested that the high contrast signals from the PEGylated Au NRs were generated via the NIR light absorption of the Au NRs within the tissue.