Electropolymerization of Preferred-Oriented Conjugated Microporous Polymer Films for Enhanced Fluorescent Sensing.

High-quality conjugated microporous polymer (CMP) films with orientation and controlled structure are extremely desired for applications. Here, we report the effective construction of CMP 3D composite films (pZn/PTPCz) with a controlled porosity structure and preferred orientation using the template-assisted electropolymerization (EP) approach for the first time. The structure of pZn/PTPCz composite thin films and nitrophenol sensing performance were thoroughly studied. When compared to the control CMP film made on flat indium tin oxide (ITO) substrates, the as-prepared pZn/PTPCz composite films showed significantly enhanced fluorescent intensity and much better sensing performance for the model explosive. This was attributed to the metal-enhanced fluorescence (MEF) of porous nanostructured zinc (pZn) and the additional macroporosity of the pZn/PTPCz composite films. This work provides a feasible approach for creating oriented 3D CMP-based thin films for advanced applications.

Size Dependence of Gold Nanorods for Efficient and Rapid Photothermal Therapy.

In recent years, gold nanomaterials have become a hot topic in photothermal tumor therapy due to their unique surface plasmon resonance characteristics. The effectiveness of photothermal therapy is highly dependent on the shape and size of gold nanoparticles. In this work, we investigate the photothermal therapeutic effects of four different sizes of gold nanorods (GNRs). The results show that the uptake of short GNRs with aspect ratios 3.3-3.5 by cells is higher than that of GNRs with aspect ratios 4-5.5. Using a laser with single pulse energy as low as 28 pJ laser for 20 s can induce the death of liver cancer cells co-cultured with short GNRs. Long GNRs required twice the energy to achieve the same therapeutic effect. The dual-temperature model is used to simulate the photothermal response of intracellular clusters irradiated by a laser. It is found that small GNRs are easier to compact because of their morphological characteristics, and the electromagnetic coupling between GNRs is better, which increases the internal field enhancement, resulting in higher local temperature. Compared with a single GNR, GNR clusters are less dependent on polarization and wavelength, which is more conducive to the flexible selection of excitation laser sources.

A DFT Study of Volatile Organic Compounds Detection on Pristine and Pt-Decorated SnS Monolayers.

Real-time monitoring of volatile organic compounds (VOCs) is crucial for both industrial production and daily life. However, the non-reactive nature of VOCs and their low concentrations pose a significant challenge for developing sensors. In this study, we investigated the adsorption behaviors of typical VOCs (C2H4, C2H6, and C6H6), on pristine and Pt-decorated SnS monolayers using density functional theory (DFT) calculations. Pristine SnS monolayers have limited charge transfer and long adsorption distances to VOC molecules, resulting in VOC insensitivity. The introduction of Pt atoms promotes charge transfer, creates new energy levels, and increases the overlap of the density of states, thereby enhancing electron excitation and improving gas sensitivity. Pt-decorated SnS monolayers exhibited high sensitivities of 241,921.7%, 35.7%, and 74.3% towards C2H4, C2H6, and C6H6, respectively. These values are 142,306.9, 23.8, and 82.6 times higher than those of pristine SnS monolayers, respectively. Moreover, the moderate adsorption energies of adsorbing C2H6 and C6H6 molecules ensure that Pt-decorated SnS monolayers possess good reversibility with a short recovery time at 298 K. When heated to 498 K, C2H4 molecules desorbs from the surface of Pt-decorated SnS monolayer in 162.33 s. Our results indicate that Pt-decorated SnS monolayers could be superior candidates for sensing VOCs with high selectivity, sensitivity, and reversibility.

Highly stable and recoverable humidity sensor using fluorescent quantum dot film.

Fluorescent sensors are resistant to electromagnetic interference and are electrically insulated, allowing for highly accurate measurements. Quantum dots (QDs) serve as outstanding sensing materials owing to the unique optical properties such as tunable photoluminescence (PL), excellent visible light activity, and high chemical and physical stability. In this paper, we develop an optical humidity sensor based on a QDs nanocomposite film. The film is made of polyvinyl alcohol (PVA), SiO2 microsphere (SM), and QDs through the layer-by-layer self-assembly method. The mechanism of humidity detection is moisture-induced quenching of the QDs fluorescence intensity. The results reveal that our sensor shows a good linear response to relative humidity in the range of 5% to 97%, a fast response-recovery time of 25 s and 20 s, and good repeatability for more than 50 cycles as well as high stability for over 180 days. Possessing the remarkable property, optical humidity sensors are envisaged for great potential applications in environmental monitoring.

Microfiber-directed reversible assembly of Au nanoparticles for SERS detection of pollutants.

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted tremendous interest as a highly sensitive label-free tool to detect pollutants in aqueous environments. However, the high cost and poor reusability of conventional SERS substrates restrict their further applications in rapid and reproducible pollutant detection. Here, we report a reliable optical manipulation method to achieve rapid photothermal self-assembly of Au nanoparticles (AuNPs) in water within 30 s by a tapered optical fiber, which is utilized for highly sensitive SERS substrate preparation. The results show that the SERS substrate achieves low detection limits of 10-9 mol/L with an enhancement factor (EF) of 106 for chemical pollutants solutions, including thiram, pyrene, and rhodamine 6G. The SERS enhancement effect based on assembled AuNPs was more than 20 times that based on a gold colloid solution. As a result, the smart reversible assembly of AuNPs exhibits switchable plasmonic coupling for tuning SERS activity, which is promising for the application of SERS-based sensors and environmental pollutant detection.

PVA-SM microstructure enhanced ratiometric fluorescence probe for formaldehyde detection in solution and gas.

Formaldehyde (FA) is one of the most common pollutants, which has tremendous harm to humans and environment. In this work, 4-amino-3-pentene-2-one (Fluoral-p) and SiO2 coated quantum dot (QD@SiO2) were combined to implement a new ratiometric fluorescence probe QD@SiO2-Fluoral-p for FA detection. In addition, by utilization of polyvinyl alcohol (PVA) and SiO2 microsphere (SM), a kind of PVA-SM microstructure was assembled with QD@SiO2-Fluoral-p to composite a signal enhanced sensing film. The QD@SiO2-Fluoral-p exhibited good response to 0-400 mg/L FA solution and an enhancement around 15 folds was realized after introducing PVA-SM. In both situations, the probe showed linear relationship to FA concentration (CFA), with detection limits of 14 and 0.5 mg/L, respectively. Also, the sensing film showed a good linear response to FA gas in the range of 0 to 2 ppm, with a detection limit 0.03 ppm. As a result, the PVA-SM enhanced ratiometric fluorescence probe features high sensitivity, low detection limit, good selectivity, as well as portable, which can serve as a useful tool for investigating FA in solution and gas at room temperature.

Photothermal microfluidic-assisted self-cleaning effect for a highly reusable SERS sensor.

The synergistic integration of optofluidic and surface enhanced Raman scattering (SERS) sensing is a new analytical technique that provides a number of unique characteristics for enhancing the sensing performance and simplifying the design of microsystems. Here, we propose a reusable optofluidic SERS sensor by integrating Au nanoisland substrate (AuNIS)-coated fiber into a microfluidic chip. Through both systematic experimental and theoretical analysis, the sensor enables efficient self-cleaning based on its optical-to-heat-hydrodynamic energy conversion property. Besides, the sensor exhibits the instrument detection limit down to 10-13mol/L and enhancement factor of 106 for Rhodamine 6G. Our optofluidic SERS sensor with such a photothermal microfluidic-assisted self-cleaning method has the advantages of portability, simple operation, and high cleaning efficiency, which will provide a new, to the best of our knowledge, concept and approach for cost-effective and reusable sensors.

Vortices-interaction-induced microstreaming for the pump-free separation of particles.

Microfluidic techniques have emerged as promising strategies for a wide variety of synthetic or biological sorting. Unfortunately, there is still a lack of sorting with automatic and handy operation. In contrast to passively generated vortices, the thermocapillary vortices produced by temperature gradient have the advantages of flexible manipulation, stable strength, and simple integration. In this Letter, we present a device used for the pump-free separation of particles through vortices interaction without external fluidic control systems required for the majority of existing devices. Specifically, the device induces a different flow type upon the actuation of optical power, and the flow functions, such as simultaneous pumping and sorting, agree with stimulation results very well. More importantly, our developed sorting device can achieve separations by means of tunable cutoff diameter size. Therefore, this versatile device can be utilized to sort complex samples with the advantages of portability, user-friendly control, and automation.

Brain Metastases of Non-Small Cell Lung Cancer: Magnetic Resonance Spectroscopy for Clinical Outcome Assessment in Patients with Stereotactic Radiotherapy.

BACKGROUND: Brain metastases (BM) are severe incidents among patients with non-small cell lung cancer (NSCLC) and have been associated with significant morbidity and decreased survival; thus, new methods are required to improve clinical management. Magnetic resonance spectroscopy (MRS) allows noninvasive measurements of biochemical information from tumor tissue, providing clinically useful imaging biomarkers. The primary aim of this study was to explore the application of MRS in the assessment of tumor prognosis after stereotactic radiotherapy in NSCLC patients with BM. PATIENTS AND METHODS: MRS was performed on NSCLC patients attending Qingdao Center Hospital with suspected BM, and 68 patients were included in the survival analysis. The qualitative and quantitative parameters of MRS metabolites, such as choline (Cho), creatine (Cr), and N-acetyl-aspartate (NAA), were recorded. To select a cutoff for MRS metabolite parameters in the tumor and to distinguish patients who had recurrence, we performed an ROC curve analysis. Univariate and multivariate Cox regression analyses were used to assess the association between MRS metabolite parameters and clinical cancer prognosis. RESULTS: The average age was 56 years. A total of 68 NSCLC patients underwent metabolic evaluation with single voxel proton MRS and were selected for retrospective analysis. According to the area under the curve (AUC) to predict recurrence, the MRS metabolite parameters were determined as Cho (AUC=0.550), Cr (AUC=0.415), NAA (AUC=0.524), NAA/Cr (AUC=0.600), Cho/Cr (AUC=0.723), and Cho/NAA (AUC=0.543). Cho and Cr predicted poor survival while Cho/Cr and NAA/Cr predicted improved survival (P<0.05). In the multivariate model with adjustment to establish the potential role of MRS metabolite parameters, Cho/Cr showed a significant association with OS (P=0.009) and PFS (P=0.006) after stereotactic radiotherapy. CONCLUSION: The positive results of this study indicate the predictive value of metabolic characteristics of BM detected with MRS for the outcome after stereotactic radiotherapy.

Generation and manipulation of oil-in-water micro-droplets by confined thermocapillary microvortices.

Optofluidic manipulation of droplets is critical in droplet-based microfluidic systems for chemistry, biology, and medicine. Here, we reported a thermocapillary microvortices-based manipulation platform for controlling oil-in-water droplets through integrating a photothermal waveguide into a microfluidic chip. The sizes and shapes of the droplets can be controlled by adjusting optical power or positions of the water-oil interface. Here, teardrop-shaped droplets, which can encapsulate and accumulate mesoscopic matters easily, were generated when the water-oil interface and the channel boundaries approached the photothermal waveguide center simultaneously. The results showed that the thermocapillary microvortices have good controllability of droplet positions, droplet volumes, and encapsulated-particle distribution and thus it will be a powerful droplet manipulation strategy for microreactors and microcapsules.

Surface Plasmon-Enhanced Optical Formaldehyde Sensor Based on CdSe@ZnS Quantum Dots.

For the first time, a reproducible surface plasmon-enhanced optical sensor for the detection of gaseous formaldehyde was proposed, which was fabricated by depositing a mixture of CdSe@ZnS quantum dots (QDs), fumed silica (FS), and gold nanoparticles (GNs) on the surface of a silica sphere array to meet the urgent requirement of a rapid, sensitive, and highly convenient formaldehyde detection method. Because of the spectral overlap between QDs and GNs, plasmon-enhanced fluorescence was observed in the film of QDs/FS/GNs. When exposed to formaldehyde molecules, the enhanced fluorescence was quenched linearly with the increase of formaldehyde concentration in the range of 0.5-2.0 ppm. The reason is attributed to the nonradiative electron transfer from QDs to the carbonyl of formaldehyde molecules with the assistance of amino groups. Our results demonstrate that the designed sensors are capable of detecting ultralow concentration gaseous formaldehyde at room temperature with a fast response-recovery time and excellent selectivity, stability, and reproducibility. This work provides a simple and low-cost approach for optical formaldehyde sensor fabrication and shows promising applications in environmental detection.

Photothermal conversion of SiO2@Au nanoparticles mediated by surface morphology of gold cluster layer.

Photothermal effects in SiO2@Au core-shell nanoparticles have demonstrated great potential in various applications for drug delivery, thermo-photovoltaics and photothermal cancer therapy, etc. However, the photothermal conversion of SiO2@Au nanoparticles partially covered by disconnected gold clusters has rarely been investigated systematically. Here, we control the surface morphology of gold clusters on the photothermal conversion performance of SiO2@Au core-shell nanoparticles by means of chemically adjusting the synthesis parameters, including amounts of gold salts, pH value and reducing agent. The macroscopic variations of the photothermal heating of different nanoparticle dispersions are significantly influenced by the nanoscale differences of gold cluster morphologies on the silica core. The temperature rise can be enhanced by the strong near-field coupling and collective heating among gold clusters with a relatively uniform distribution on the silica core. A numerical model of the simplified photothermal system is formulated to interpret the physical mechanism of the experimental observation, and shows a similar trend of temperature rise implying a reasonably good agreement with experimental data. Our work opens new possibilities for manipulating the light-to-heat conversion performance of SiO2@Au core-shell nanoparticles and potential applications of heat delivery with spatial resolution on the nanoscale.

Strain-engineering the in-plane electrical anisotropy of GeSe monolayers.

As a representative in-plane anisotropic two-dimensional (2D) material, germanium monoselenide (GeSe) has attracted considerable attention recently due to its various in-plane anisotropic material properties originating from the low symmetry of a puckered honeycomb structure. Although there have been plenty of reports on the in-plane anisotropic vibrational, electrical and optical properties of GeSe, the strain effect on those appealing anisotropies is still under exploration. Here we report a systematic first-principles computational investigation of strain-engineering of the anisotropic electronic properties of GeSe monolayers. We found that the anisotropic ratio of the effective mass and mobility of charge carriers (electrons and holes) of GeSe along two principle axes can be controlled by using simple strain conditions. Notably, the preferred conducting direction of GeSe can be even rotated by 90° under an appropriate uniaxial strain (>5%). Such effective strain modulation of the electronic anisotropy of GeSe monolayers provides them abundant opportunities for future mechanical-electronic devices.

Miniaturized optical fiber tweezers for cell separation by optical force.

In advanced biomedicine and microfluidics, there is a strong desire to sort and manipulate various cells and bacteria based on miniaturized microfluidic chips. Here, by integrating fiber tweezers into a T-type microfluidic channel, we report an optofluidic chip to selectively trap Escherichia coli in human blood solution based on different sizes and shapes. Furthermore, we simulate the trapping and pushing regions of other cells and bacteria, including rod-shaped bacteria, sphere-shaped bacteria, and cancer cells based on finite-difference analysis. With the advantages of controllability, low optical power, and compact construction, the strategy may be possibly applied in the fields of optical separation, cell transportation, and water quality analysis.

Coexistence of rectangular and Gaussian-shape noise-like pulses in a figure-eight fiber laser.

We experimentally report the coexistence of the rectangular noise-like pulse (NLP) and the Gaussian-shape NLP in a figure-eight fiber laser. Benefiting from the strengthened nonlinear effect of a segment of highly nonlinear fiber (HNLF) in the cavity, the coexistent NLPs with various patterns, i.e. one rectangular pulse with one Gaussian-shape pulse, one rectangular pulse with two Gaussian-shape pulses and two rectangular pulses with one Gaussian-shape pulse, are formed depending on the cavity parameters setting. In particular, the evolution of these coexistent NLPs properties with pump power is investigated. It is found that the duration of the rectangular pulse always increases, while the Gaussian-shape pulse has almost no changes with the increasing pump power. The achieved results demonstrated for the first time, to the best of our knowledge, the pulses with different shapes can coexist under the NLP regime, which contributes to further understanding the fundamental characteristics of the NLPs and multiple pulses.

Strain-engineering the electronic properties and anisotropy of GeSe2 monolayers.

As a new two-dimensional (2D) material, GeSe2 has attracted significant attention recently due to its distinctive in-plane anisotropic properties originated from the in-plane anisotropic crystal structure, high air stability and excellent performance in polarization-sensitive photodetection. However, no systematic study of the strain effect on the electronic properties and anisotropy of GeSe2 has been reported, restricting the relevant applications such as mechanical-electronic devices. Here we investigate the change of the electronic properties and anisotropy of GeSe2 monolayer under strains along x and y directions through first-principle calculations. The electronic band structure and effective mass of charge carriers are highly sensitive to the strain. Notably, through appropriate x or y directional strain, the anisotropy of the hole effective mass can even be rotated by 90°. These plentiful strain-engineering properties of GeSe2 give it many opportunities in novel mechanical-electronic applications.

High throughput trapping and arrangement of biological cells using self-assembled optical tweezer.

Lately, a fiber-based optical tweezer that traps and arranges the micro/nano-particles is crucial in practical applications, because such a device can trap the biological samples and drive them to the designated position in a microfluidic system or vessel without harming them. Here, we report a new type of fiber optical tweezer, which can trap and arrange erythrocytes. It is prepared by coating graphene on the cross section of a microfiber. Our results demonstrate that thermal-gradient-induced natural convection flow and thermophoresis can trap the erythrocytes under low incident power, and the optical scattering force can arrange them precisely under higher incident power. The proposed optical tweezer has high flexibility, easy fabrication, and high integration with lab-on-a-chip, and shows considerable potential for application in various fields, such as biophysics, biochemistry, and life sciences.

Detection of microRNA in clinical tumor samples by isothermal enzyme-free amplification and label-free graphene oxide-based SYBR Green I fluorescence platform.

MicroRNAs (miRNAs) are a kind of small molecules that involve in many important life activities. They have higher expression levels in many kinds of cancers. In this study, we developed an isothermal enzyme-free amplification (EFA) and label-free graphene oxide (GO)-based SYBR Green I fluorescence platform for detection of miRNA. MiRNA-21 was used as an example to demonstrate the feasibility of the method. Results show that the sensitivity of miRNA-21 is 1pM, and the linearity range is from 1pM to 1nM. The method can specifically discriminate miRNA-21 from miRNA-210 and miRNA-214. Three tumor cell lines of A549, HepG2 and MCF7 were detected by the method. The sensitivities of them were 10(2) cells, 10(3) cells and 10(3) cells respectively. Clinical tumor samples were also tested by this method, and 29 of 40 samples gave out positive signals. The method holds great promise in miRNA detection due to its convenience, rapidness, inexpensive and specificity.

Dynamic behaviors of approximately ellipsoidal microbubbles photothermally generated by a graphene oxide-microheater.

Thermal microbubbles generally grow directly from the heater and are spherical to minimize surface tension. We demonstrate a novel type of microbubble indirectly generated from a graphene oxide-microheater. Graphene oxide's photothermal properties allowed for efficient generation of a thermal gradient field on the microscale. A series of approximately ellipsoidal microbubbles were generated on the smooth microwire based on heterogeneous nucleation. Other dynamic behaviors induced by the microheater such as constant growth, directional transport and coalescence were also investigated experimentally and theoretically. The results are not only helpful for understanding the bubble dynamics but also useful for developing novel photothermal bubble-based devices.

Graphene oxide-deposited microfiber: a new photothermal device for various microbubble generation.

This study makes a claim of utilizing the photothermal effect of graphene oxide nanosheets (GONs) to effectively produce various microbubbles in an optical microfiber system at infrared optical communications band. A low power continuous-wave light at wavelength of 1527-1566 nm was launched into the microfiber to form GONs-deposition which acted as a linear heat source for creating various microbubbles. Both thermal convection flow and optical gradient force were responsible for the driving force to assemble GONs onto the microfiber. This simple optical fiber system can be used for assembling other micro/nanoscale particles and biomolecules, which has prospective applications in sensing, microfluidics, virus detection, and other biochip techniques.