Study of cell and drug interactions based on dual-mode detection using SPR and fluorescence imaging.

The investigation of the interactions between cells and drugs forms a crucial aspect of biological and clinical medical studies. Generally, single-cell or local-cellular studies require a microscopic imaging system with high magnifications, which suffers from low detection throughputs and poor time responses. The study presented in this paper combined SPR and fluorescence to achieve cell localization, real-time monitoring of cell images and quantitative analysis of drugs. In order to obtain more comprehensive, accurate and real-time data, a dual-mode system based on surface plasmon resonance (SPR) and fluorescence was constructed based on a 4× magnification lens. This enables simultaneous studies of an entire cell and a specific region of the cell membrane. An adaptive adjustment algorithm was established for distorted SPR images, achieving temporal and spatial matching of the dual-mode detection. The combination of SPR and fluorescence not only achieved micro-detection but also complemented the qualitative or quantitative limitations of SPR or fluorescence method alone. In system characterization, the response signal of SPR was noticed to increase with the increasing concentration of EGF in stimulated cells. It indicated that this platform could be employed for quantitative detection of the cell membrane region. Upon addition of EGF, a peak in the SPR curve was observed, and the cells in the corresponding SPR image turned whiter. This indicated that the platform can simultaneously monitor the SPR response signal and image changes. The response time of fluorescence in EGF testing was several seconds earlier than SPR, revealing that signal transduction first occurred in the whole cell and then propagated to the cell membrane region. The inhibitory ability of Gefitinib on cells was verified in a fast and real-time manner within 20 min. The results indicated that the detection limit of this method was 20 IU/mL for EGF and 10 µg/mL for Gefitinib. In conclusion, this study demonstrates the advantages of SPR and fluorescence dual-mode techniques in the analysis of cell-drug interactions, as well as their strong potential in drug screening.

Cu-doped SnO2/rGO nanocomposites for ultrasensitive H2S detection at low temperature.

Hydrogen sulfide (H2S) detection remains a significant concern and the sensitivity, selectivity, and detection limit must be balanced at low temperatures. Herein, we utilized a facile solvothermal method to prepare Cu-doped SnO2/rGO nanocomposites that have emerged as promising candidate materials for H2S sensors. Characterization of the Cu-SnO2/rGO was carried out to determine its surface morphology, chemical composition, and crystal defects. The optimal sensor response for 10 ppm H2S was ~1415.7 at 120 °C, which was over 320 times higher than that seen for pristine SnO2 CQDs (Ra/Rg = 4.4) at 280 °C. Moreover, the sensor material exhibited excellent selectivity, a superior linear working range (R2 = 0.991, 1-150 ppm), a fast response time (31 s to 2 ppm), and ppb-level H2S detection (Ra/Rg = 1.26 to 50 ppb) at 120 °C. In addition, the sensor maintained a high performance even at extremely high humidity (90%) and showed outstanding long-term stability. These superb H2S sensing properties were attributed to catalytic sensitization by the Cu dopant and a synergistic effect of the Cu-SnO2 and rGO, which offered abundant active sites for O2 and H2S absorption and accelerated the transfer of electrons/holes.

All-day uninterrupted thermoelectric generator by simultaneous harvesting of solar heating and radiative cooling.

Passive power generation has recently stimulated interest in thermoelectric generators (TEGs) using the radiative cooling mechanism. However, the limited and unstable temperature difference across the TEGs significantly degrades the output performance. In this study, an ultra-broadband solar absorber with a planar film structure is introduced as the hot side of the TEG to increase the temperature difference by utilizing solar heating. This device not only enhances the generation of electrical power but also realizes all-day uninterrupted electrical output due to the stable temperature difference between the cold and hot sides of the TEG. Outdoor experiments show the self-powered TEG obtains maximum temperature differences of 12.67 °C, 1.06 °C, and 5.08 °C during sunny daytime, clear nighttime, and cloudy daytime, respectively, and generates output voltages of 166.2 mV, 14.7 mV, and 95 mV, respectively. Simultaneously, the corresponding output powers of 879.25 mW/m2, 3.85 mW/m2, and 287.27 mW/m2 are produced, achieving 24-hour uninterrupted passive power generation. These findings propose a novel strategy to combine solar heating and outer space cooling by a selective absorber/emitter to generate all-day continuous electricity for unsupervised small devices.

Wearable and flexible electrochemical sensors for sweat analysis: a review.

Flexible wearable sweat sensors allow continuous, real-time, noninvasive detection of sweat analytes, provide insight into human physiology at the molecular level, and have received significant attention for their promising applications in personalized health monitoring. Electrochemical sensors are the best choice for wearable sweat sensors due to their high performance, low cost, miniaturization, and wide applicability. Recent developments in soft microfluidics, multiplexed biosensing, energy harvesting devices, and materials have advanced the compatibility of wearable electrochemical sweat-sensing platforms. In this review, we summarize the potential of sweat for medical detection and methods for sweat stimulation and collection. This paper provides an overview of the components of wearable sweat sensors and recent developments in materials and power supply technologies and highlights some typical sensing platforms for different types of analytes. Finally, the paper ends with a discussion of the challenges and a view of the prospective development of this exciting field.

Theoretical and experimental study of a highly sensitive SPR biosensor based on Au grating and Au film coupling structure.

A high-sensitivity surface plasmon resonance (SPR) sensor based on the coupling of Au grating and Au film is investigated through simulations and experiments. The SPR sensor is designed by using a hybrid method composed of genetic algorithm (GA) and rigorous coupled wave analysis (RCWA). The numerical results indicate the sensor has an angular sensitivity of 397.3°/RIU (refractive index unit), which is approximately 2.81 times higher than the conventional Au-based sensor and it is verified by experiments. Theoretical analysis, by finite-difference time-domain (FDTD) method, demonstrates the co-coupling between surface plasmon polaritons (SPPs) propagating on the surface of Au film and localized surface plasmons (LSPs) in the Au grating nanostructure, improving the sensitivity of the SPR sensor. According to the optimized structural parameters, the proposed sensor is fabricated using e-beam lithography and magnetron sputtering. In addition, the proposed sensor is very sensitive to the detection of small molecules. The limit of detection (LOD) for okadaic acid (OA) is 0.72 ng/mL based on an indirect competitive inhibition method, which is approximately 38 times lower than the conventional Au sensor. Such a high-sensitivity SPR biosensor has potential in the applications of immunoassays and clinical diagnosis.

Design of multilayer planar film structures for near-perfect absorption in the visible to near-infrared.

In this work, a near-perfect broadband absorber, consisting of Fe, MgF2, Fe, TiO2 and MgF2 planar film, is proposed and investigated through simulations and experiments. The Fe material is first applied in the multilayer film structure, and it is proved to be more favorable for achieving broadband absorption. MgF2 and TiO2 are chosen as anti-reflection coatings to decrease unwanted reflections. The proposed absorber is optimized by employing a hybrid numerical method combining the transfer matrix method (TMM) and the genetic algorithm (GA). Under normal incidence conditions, the average absorption of the absorber is 97.6% in the range of 400 to 1400 nm. The finite difference time domain (FDTD) method and phase analysis reveal that the anti-reflection property and the Fabry-Perot resonance result in broadband absorption performance. Furthermore, when an additional Fe-MgF2 layer is inserted on the bottom Fe layer, an average absorption of 97.9% in the range of 400 to 2000 nm can be achieved. Our approach could be of vital significance for numerous applications involving solar energy.

Performance Enhancement of SPR Biosensor Using Graphene-MoS2 Hybrid Structure.

We investigate a high-sensitivity surface plasmon resonance (SPR) biosensor consisting of a Au layer, four-layer MoS2, and monolayer graphene. The numerical simulations, by the transfer matrix method (TMM), demonstrate the sensor has a maximum sensitivity of 282°/RIU, which is approximately 2 times greater than the conventional Au-based SPR sensor. The finite difference time domain (FDTD) indicates that the presence of MoS2 film generates a strong surface electric field and enhances the sensitivity of the proposed SPR sensor. In addition, the influence of the number of MoS2 layers on the sensitivity of the proposed sensor is investigated by simulations and experiments. In the experiment, MoS2 and graphene films are transferred on the Au-based substrate by the PMMA-based wet transfer method, and the fabricated samples are characterized by Raman spectroscopy. Furthermore, the fabricated sensors with the Kretschmann configuration are used to detect okadaic acid (OA). The okadaic acid-bovine serum albumin bioconjugate (OA-BSA) is immobilized on the graphene layer of the sensors to develop a competitive inhibition immunoassay. The results show that the sensor has a very low limit of detection (LOD) of 1.18 ng/mL for OA, which is about 22.6 times lower than that of a conventional Au biosensor. We believe that such a high-sensitivity SPR biosensor has potential applications for clinical diagnosis and immunoassays.

High Sensitivity Surface Plasmon Resonance Sensor Based on Periodic Multilayer Thin Films.

Surface plasmon resonance (SPR) biosensors consisting of alternate layers of silver (Ag) and TiO2 thin film have been proposed as a high sensitivity biosensor. The structure not only prevents the Ag film from oxidation, but also enhances the field inside the structure, thereby improving the performance of the sensor. Genetic algorithm (GA) was used to optimize the proposed structure and its maximum angular sensitivity was 384°/RIU (refractive index unit) at the refractive index environment of 1.3425, which is about 3.12 times that of the conventional Ag-based biosensor. A detailed discussion, based on the finite difference time domain (FDTD) method, revealed that an enhanced evanescent field at the top layer-analyte region results in the ultra-sensitivity characteristic. We expect that the proposed structure can be a suitable biosensor for chemical detection, clinical diagnostics, and biological examination.

Hand Gesture Recognition on a Resource-Limited Interactive Wristband.

Most of the reported hand gesture recognition algorithms require high computational resources, i.e., fast MCU frequency and significant memory, which are highly inapplicable to the cost-effectiveness of consumer electronics products. This paper proposes a hand gesture recognition algorithm running on an interactive wristband, with computational resource requirements as low as Flash < 5 KB, RAM < 1 KB. Firstly, we calculated the three-axis linear acceleration by fusing accelerometer and gyroscope data with a complementary filter. Then, by recording the order of acceleration vectors crossing axes in the world coordinate frame, we defined a new feature code named axis-crossing code. Finally, we set templates for eight hand gestures to recognize new samples. We compared this algorithm's performance with the widely used dynamic time warping (DTW) algorithm and recurrent neural network (BiLSTM and GRU). The results show that the accuracies of the proposed algorithm and RNNs are higher than DTW and that the time cost of the proposed algorithm is much less than those of DTW and RNNs. The average recognition accuracy is 99.8% on the collected dataset and 97.1% in the actual user-independent case. In general, the proposed algorithm is suitable and competitive in consumer electronics. This work has been volume-produced and patent-granted.

Layer analysis of axial spatial distribution of surface plasmon resonance sensing.

The spatial distribution detection and characterization of multi-adsorption layers, biomembranes, and cells are important techniques to study biomolecular properties and mechanisms. Using the surface plasmon resonance (SPR) technology, we investigated the spatial characteristics, penetration mechanism, and detection depth of the interaction between evanescent waves and a complex medium. In addition, parameters correlated with the axial spatial distribution were analyzed. We found that the spatial refractive-index distribution of an axial layered model has a unique correlation with the following three characteristic parameters: resonance angle at different wavelengths, first-derivative extreme-point of the angular spectrum, and effective refractive index. A new layer-analysis, based on wavelength-scanning angle interrogation (WSAI), was introduced to enable refractive-index measurements in an axial spatial medium. This new method extends the detection capabilities of SPR sensors and provides a more accurate analysis method for interaction events within an evanescent field.

Design of an ultra-broadband near-perfect bilayer grating metamaterial absorber based on genetic algorithm.

An ultra-broadband metamaterial absorber, consisting of 2D SiO2-Ti square bilayer grating on SiO2 film and Ti substrate, is proposed and designed by rigorous coupled wave analysis (RCWA) and genetic algorithm (GA) methods. The optimized structure shows an average absorption of 98.3% in the wavelength range of 300 nm to 2100 nm. Moreover, the metamaterial absorber is polarization-independent and also insensitive to incidence angle for both TM- and TE-polarized waves. The physical mechanisms responsible for nearly perfect broadband absorption, including the Wood's anomaly (WA), cavity resonance (CR), surface plasmon polaritons (SPPs) and the resonance of magnetic polaritons (MPs), have been analyzed clearly by finite-difference time-domain (FDTD) method and the inductor-capacitor (LC) circuit model. Overall, the proposed metamaterial absorber is a promising candidate in solar applications.

Nanoparticles Enhanced Self-driven Microfludic Biosensor.

C-reactive protein (CRP) plays an important role in inflammation detection and disease monitoring. The optical biosensor is a highly sensitive and easy detection tool. The microfluidic self-driving optical sensors were fabricated with transparent glass material and used for the enhanced surface plasmon resonance (SPR) optical detection of the model protein CRP using Au nanoparticles (AuNPs) and a sandwich immune reaction. The 3D design of the chip was devised to improve the optical coupling efficiency and enable integration with a microfluidic control and rapid detection. The array of pre-fixed antibody modified by Au nanoparticles was used to achieve rapid antigen capture and improve the optical sensitivity. The Au nanoparticle amplification approach was introduced for the SPR detection of a target protein. CRP was used as a model target protein as part of a sandwich assay. The use of Au NP measurements to detect the target signal is a threefold improvement compared to single SPR detection methods.

Facile one-step synthesis of onion-like carbon modified ultrathin g-C3N4 2D nanosheets with enhanced visible-light photocatalytic performance.

Herein, novel mesoporous carbon-doped g-C3N4 ultrathin nanosheets (C/CNNS) have been synthesized for the first time through a facile one-step thermal condensation method using agar-melamine gel (AMG) as precursor. A series of characterizations were carried out to explore the structure, morphology and optoelectronic properties of the C/CNNS photocatalyst. The resultant C/CNNS-0.5 exhibited the optimum photocatalytic performance with respect to bulk g-C3N4 by using Rhodamine B, Phenol, Bisphenol A and Phenanthrene as target pollutants under visible light irradiation. Such remarkable enhancement of photocatalytic activity was mainly attributed to the synergistic effect of onion-like carbon (OLC) and ultrathin 2D nanosheets structure. The introduction of OLC could effectively expand visible-light absorption regions. Besides, OLC can act as an electron receiver to facilitate charge separation and inhibit the recombination of photogenerated carriers. 2D nanosheets structure provides more active sites for photocatalytic reactions, which further improve photocatalytic activity of C/CNNS-0.5 photocatalyst. The photocatalytic mechanism of C/CNNS for removing organic pollutants was explored by electron spin resonance (ESR) technique. Much different from the bulk g-C3N4, superoxide radical (O2-) and hydroxyl radical (OH) were the two main radicals, while for the bulk g-C3N4, there is only the O2- radical worked in the photocatalytic reaction.

Research on highly sensitive optomagnetic sensor for rapid detection of inflammation.

BACKGROUND: C-reactive protein (CRP) is used to evaluate the evolution of infections and sepsis in critically ill patients. For POCT testing, biosensor-based detection techniques offer quick and convenient application. OBJECTIVE: A prototype three dimensional chip was fabricated based on a new optomagnetic method to achieve the rapid detection of CRP. METHODS: This work investigates a new technology for the quick quantitative detection of the C-reactive protein (CRP) by total internal reflection magnetic imaging (TIRMI) on a three dimensional optomagnetic sensor. Transparent glass and hydrophilic plastic film with channels were used to construct the three dimensional sensor. The magnetic nanoparticles and immunological reagent were immobilized on the reaction area of the sensor. Samples were detected using total internal reflection magnetic spot imaging (TIRMI) based on a sandwich magnetic immunoassay by one-step assay. RESULTS: The developed 3D biosensor-TIRMI method showed a wide dynamic linear range (0.2-200 ng/ml) and quick detection (5 min) with low-sample volume (10 µL). CONCLUSIONS: We have presented a three dimensional optical protein chip that fulfills the demanding for point-of-care diagnostics in terms of ease-of-use (one step assay), miniaturization, assay time. This approach shows great promise for application in clinical investigations of biological samples.

Generation of Localized Surface Plasmon Resonance Using Hybrid Au-Ag Nanoparticle Arrays as a Sensor of Polychlorinated Biphenyls Detection.

In this study, the hybrid Au-Ag hexagonal lattice of triangular and square lattice of quadrate periodic nanoparticle arrays (PNAs) were designed to investigate their extinction spectra of the localized surface plasmon resonances (LSPRs). First, their simulating extinction spectra were calculated by discrete dipole approximation (DDA) numerical method by changing the media refractive index. Simulation results showed that as the media refractive index was changed from 1.0 to 1.2, the maximum peak intensity of LSPRs spectra had no apparent change and the wavelength to reveal the maximum peak intensity of LSPRs spectra was shifted lower value. Polystyrene (PS) nanospheres with two differently arranged structures were used as the templates to deposit the hybrid Au-Ag hexagonal lattice of triangular and square lattice of quadrate periodic PNAs by evaporation method. The hybrid Au-Ag hexagonal lattice of triangular and square lattice of quadrate PNAs were grown on single crystal silicon (c-Si) substrates, and their measured extinction spectra were compared with the calculated results. Finally, the fabricated hexagonal lattices of triangular PNAs were investigated as a sensor of polychlorinated biphenyl solution (PCB-77) by observing the wavelength to reveal the maximum extinction efficiency (λmax). We show that the adhesion of ß-cyclodextrins (SH-ß-CD) on the hybrid Au-Ag hexagonal lattice of triangular PNAs could be used to increase the variation of λmax. We also demonstrate that the adhesion of SH-ß-CD increases the sensitivity and detection effect of PCB-77 in hexagonal lattice of triangular PNAs.

Fabrication and characterization of microelectromechanical systems-based gas chromatography column with embedded micro-posts for separation of environmental carcinogens.

In this paper, a micro gas chromatography (µGC) column with embedded micro-posts was developed for increasing overall surface area of the columns which is able to support more of the stationary phase and reducing the effective width of the column, leading to higher separation efficiency. The proposed columns have a higher sample capacity as the overall surface area is about 3 times larger than that of open columns with the same dimensions. In order to achieve an even flow velocity in the channels, the location of the micro-posts in the linear channels and the configuration of curved channels were optimized by numerical simulation. The results have indicated that the proposed column separated 5 environmental carcinogens in less than 50s, achieved a separation efficiency of about 9500plates/m and eluted highly symmetrical Gaussian peaks.

Use of surface plasmon resonance to investigate lateral wall deposition kinetics and properties of polydopamine films.

Dopamine (DA) is a particularly important neurotransmitter. Polydopamine (pDA) films have been demonstrated to be important materials for the immobilization of biomolecules onto almost any type of solid substrate. In this study, a surface plasmon resonance (SPR)-based sensor system with the sensor chip surface parallel to the direction of gravity was used to investigate the lateral wall deposition kinetics and properties of pDA films. The deposition kinetics of pDA Films are limited by the oxidation process. The pDA film could not be removed from the sensor chip completely by a strongly alkaline solution, indicating that the pDA film was heterogeneous in the direction of deposition. The pDA film formed near the interior of the solution was less stable than the film formed near the gold-solution interface. Adsorption of proteins on pDA film was studied compared with that on bare gold and dextran sensor chip. The reduction of Au(111) cations by the pDA film, forming a layer of gold particles, was monitored using SPR.

Effect of comonomer content on the crystallization kinetics and morphology of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

Crystallization kinetics and morphology of biodegradable poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) containing 7, 10 and 18 mol% 3-hydroxyhexanoate (HHx) comonomer were investigated by differential scanning calorimetry, polarized optical microscopy and wide angle X-ray diffraction in detail in this work. The experimental results indicate that overall isothermal crystallization rates of PHBHHx copolymers are reduced with increasing crystallization temperature and HHx content; however, the crystallization mechanism remains unchanged. Moreover, the equilibrium melting point temperatures of PHBHHx copolymers decrease with increasing the HHx content. Banded spherulites morphology and spherulitic growth rates of PHBHHx have been studied in a wide crystallization temperature range. Both band spacing and spherulite growth rate decrease with increasing the HHx comonomer content. All the investigated PHBHHx copolymers exhibit a crystallization regime II to III transition, and the crystallization regime transition temperature shifts to low temperature range with increasing the HHx content. In addition, increasing the HHx content does not modify the crystal structure or crystal cell parameters but decreases the crystallinity of PHBHHx.

A rigid poly(dimethylsiloxane) sandwich electrophoresis microchip based on thin-casting method.

We present a novel concept of glass/poly(dimethylsiloxane) (PDMS)/glass sandwich microchip and developed a thin-casting method for fabrication. Unlike the previously reported casting method for fabricating PDMS microchip, several drops of PDMS prepolymer were first added on the silanizing SU-8 master, then another glass plate was placed over the prepolymer as a cover plate, and formed a glass plate/PDMS prepolymer/SU-8 master sandwich mode. In order to form a thin PDMS membrane, a weight was placed on the glass plate. After the whole sandwich mode was cured at 80 degrees C for 30 min, the SU-8 master was easily peeled and the master microstructures were completely transferred to the PDMS membrane which was tightly stuck to the glass plate. The microchip was subsequently assembled by reversible sealing with the glass cover plate. We found that this PDMS sandwich microchip using the thin-casting method could withstand internal pressures of >150 kPa, more than 5 times higher than that of the PDMS hybrid microchip with reversible sealing. In addition, it shows an excellent heat-dissipating property and provides a user-friendly rigid interface just like a glass microchip, which facilitates manipulation of the microchip and fix tubing. As an application, PDMS sandwich microchips were tested in the capillary electrophoresis separation of fluorescein isothiocyanate-labeled amino acids.

A SU-8/PDMS hybrid microfluidic device with integrated optical fibers for online monitoring of lactate.

A microfluidic device with integrated optical fibres was developed for online monitoring of lactate. The device consists of a SU-8 waveguide, microfluidic channels and grooves for the insertion of optic fibres. It was fabricated by one-step photolithography of SU-8 polymer resist. Different channel widths (50-300 microm) were tested in terms of detection sensitivity. A wide range of flow rates were applied to investigate the influence of flow rate on signal fluctuations. The separation between optical fibre sensor and microfluidic channel and the width of fluidic channel have been optimized to maximize the detection sensitivity. It was revealed that 250 microm of channel width is the optimum light path length for a compromise between detection sensitivity and interference of ambient light. The independence of detection signals on flow rates was demonstrated within the range of flow rate (0.5-5 ml/hr) tested. Compared with conventional lactate detection, the device is proved to have high accuracy, relatively low limit of detection (50 mg/L) and reasonably fast response time (100 sec). The fabrication of device is simple and low cost. The present work has provided some fundamental data for further system optimization to meet specific detection requirements.