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Atmospheric gas discharge is very likely to constrict into filaments and diffuse plasma formation is inefficient in most cases. Developing cost-efficient atmospheric diffuse plasma devices represents a significant challenge for high performance in biomedical decontamination and material processing. Here, we propose an alternative roadmap to produce a diffuse argon plasma jet by expanding and quenching the existing filamentary discharge at the initial or middle stage of streamer development. Possible mechanisms are summarized. With the gas flow velocity comparable to the ion drift one, enhancing ambipolar diffusion near the edge of the positive-streamer channel promotes the radial diffusion of newly-produced electrons, realizing the radial expansion of channel. Weakening electric field in front of the streamer head through head expansion and field offset, prevents the further development of streamer, leading to a positive-pseudo-streamer discharge. Reducing electric field in front of the negative-streamer head through ion compensation, impedes the initial growth of streamer, resulting in a negative pulseless glow discharge. The positive-pseudo-streamer and negative pulseless glow discharges function together to form the diffuse plasma jet. Streamer coupling theory is traditionally used to engineer the generation of diffuse plasmas in the regime preceding filamentary discharge, but this method remains inefficient. Here, an alternative route to cost-efficient diffuse plasma generation is proposed, involving the expansion and quenching of existing filamentary discharge.

Current industrial production of HNO3 relies on the Ostwald process via catalytic oxidation of NH3 , which is responsible for the vast bulk of CO2 emission. An attractive alternative route to HNO3 is direct N2 oxidation to aqueous HNO3 , which avoids the NH3 intermediate. Herein, we for the first time report a non-thermal plasma-assisted nitrogen fixation process characteristic of a large gas-liquid contact based on the water falling film dielectric barrier discharge, wherein HNO3 is produced directly from ambient air and H2 O at atmospheric pressure and room temperature without the presence of any catalytic material. By optimizing the plasma reaction conditions, a relatively high synthesis rate and low energy consumption was achieved at the same time with good product selectivity.

In this study, an innovative rapid detection technology for quickly screening and quantifying organophosphorus pesticides (OPPs) in vegetables was developed based on ambient micro-fabricated glow discharge plasma desorption/ionization mass spectrometry (MFGDP-MS), where Fe3O4/ZrO2 synthesized by a one-step coprecipitation was used for enrichment. It can not only effectively enrich OPPs, but can be separated by an external magnetic field, thereby simplifying the traditional steps of centrifugation and cleanup in sample preparation. The introduction of a temperature control system (TCS) can tackle the problem of the low ionization efficiency in MFGDP and expand its application range. Under optimized experimental conditions, the limits of detection (LODs) of the standard solution as low as 0.0068-0.7500 μg L-1 mm-2 were achieved, with relative standard deviations (RSDs) being less than 17.8%. Moreover, vegetable extracts were spiked to evaluate the accuracy of the method, and good recoveries (76.9-123.5%) were obtained. Remarkably, it took no more than 7 minutes from sample preparation to testing, resulting in significantly improved ability of the quantitative detection of plentiful samples.

In recent years, the low sensitivity caused by plasma quenching has restricted the development of LIBS technology in practical applications. In order to improve the sensitivity of the LIBS analysis method, we proposed a nanoparticle-assisted metal–organic framework (MOF) enhanced laser-induced breakdown spectroscopy, which combines a metal–organic framework (MOF), Au nanoparticles (AuNPs), and a portable LIBS instrument. Common metal ions in water were selected as the research objects to be tested by the proposed method. First, the synthesized three-dimensional (3D) MOF, namely [Zn2(L2)]2DMA·3H2O (complex 1) [H2L = 2-(imidazole-1-yl)terephthalic acid], was used to capture metal ions. Second, complex 1 loaded with metal ions induced AuNPs to aggregate on its surface. Third, the samples were attached to the glass substrate with double-sided tape and analyzed by LIBS. As a result, the limits of detection (LODs) for Pb and Cr obtained in this work were 8.0 and 4.2 ng mL−1, respectively, which were notably 8–10 times lower than those of the complex 1 enrichment method alone and 4 orders of magnitude lower than those of traditional LIBS methods. The significant improvement in LODs was also a new breakthrough for LIBS in liquid analysis. The great improvement in sensitivity can be mainly attributed to the unique microporous structure and the exposed metal binding sites of complex 1, which provide a huge space to accommodate metal ions. Also, the coupling action between laser electromagnetic fields and the surface plasmon of AuNPs greatly improved the laser ablation efficiency in the process of laser–matter interaction. Finally, the analysis of actual samples yielded good recoveries (92.8–99.0%) and reproducibility (lower than 11.9%), which shows the great potential of the combination of this method and portable LIBS in-field detection.

Heavy metal ion-induced water pollution has become a severe environmental problem in the world. Although providing a powerful technique for multi-element detection, laser-induced breakdown spectroscopy (LIBS) suffers from insufficient sensitivity for detecting heavy metal ions in aqueous solution due to water splashing and surface ripples. In this work, a simple and sensitive method called gold nanoparticle (AuNP) surface-enhanced laser-induced breakdown spectroscopy (SELIBS) was proposed to detect trace or ultra-trace heavy metal ions in aqueous solutions using a portable instrument. Firstly, the coulombic force allows the adhesion of negatively charged AuNPs and cationic amphiphilic solutions to capture heavy ions, thereby directly improving signal intensity. Interestingly, AuNP size-dependent signal enhancement was found in heavy metal ions through LIBS. To be specific, the signal intensity of Cu, Pb, and Cr increased by 9, 23, and 26 times, respectively, under the optimal AuNP size with a diameter of 13 nm compared to that of the pure target solution. Although the sizes of AuNPs did not affect the plasma temperature and electron density, the local electric field and coulombic force effectively enhanced the LIBS signal. Under optimized experimental conditions, the proposed method achieves sensitive detection of heavy metal ions of Cu, Pb, and Cr with low detection limits (LODs) of 5 ng mL−1, 22 ng mL−1, and 9 ng mL−1, respectively. Moreover, the recoveries of all analytical elements in environmental water samples were analyzed by the standard addition method. The recoveries were in the range of 92.70–100.19%, which further proves the feasibility and potential of surface-enhanced laser-induced breakdown spectroscopy of AuNPs in analyzing actual liquid samples.

Rapid detection and efficient removal of heavy metal ions from environmental water are of considerable importance to tackle the water pollution problem. In this work, a simple but efficient strategy named metal-chelate induced nanoparticle aggregation enhanced laser-induced breakdown spectroscopy (MINAELIBS) was proposed for signal enhancement aiming at ultra-sensitive detection of trace levels of metal elements in liquid samples. Unlike the surface contact approach previously reported in the literature, direct mixing of gold nanoparticles (AuNPs) and metal chelates increased the contact area, adhesion force, and uniformity between analytes and AuNPs. As a result, under the optimal conditions, the limits of detection (LODs) of Cd, Cu, Ag, Pb, and Cr were 4.6, 1.5, 3.4, 3.5, and 3.5 ng mL−1, respectively. The LODs of target elements were notably 7–10 times lower than those of chelating reagent enrichment alone and 3–4 orders of magnitude lower compared to traditional LIBS methods, which demonstrates the feasibility of MINAELIBS in analysis of liquid samples at the ppb level. Application of AuNPs for high-performance signal enhancement has undoubtedly pushed the method sensitivity of traditional LIBS analyses to a new level. In addition, the recoveries of all the analytical elements in the environmental water samples were in the range from 88.6% to 109.9%, which further proves the feasibility and potential of MINAELIBS in practical liquid sample analysis.

As photonic crystals (PCs) are one of the most widely studied artificial biomimetic periodic nanostructures, their preparation methods have attracted significant attention. Recently, several methods have been developed for the self-assembly of PCs at solid and air/water interfaces. However, to date, their self-assembly at a hydrogel interface (HI) with special properties has not been explored and that at an air/gel interface is also rarely reported. Herein, a simple and novel strategy for the rapid self-assembly of PCs using a HI as an assembly interface is demonstrated. This approach is completely different from the preparation strategy of polymerized crystalline colloidal arrays (PCCAs), which involves the entrapment of a colloidal array inside a gel. Unlike the self-assembly at solid or air/water interfaces, the proposed method is faster and simpler and has the ability to prepare three-dimensional (3D) PCs on flat or curved surfaces. The reflection intensity of the hydrogel interface-photonic crystals (HI-PCs) could exceed 80%. Particularly, the transmissivity at a specific wavelength reached as low as 0.1%. Therefore, with the recent progress in the self-assembly of interfaces, soft matter interfaces, such as a hydrogel interface, will play an important new role, which is expected to open up an interesting field of research and provide more ideas for the preparation of advanced materials.

Widespread use of organophosphorus pesticides poses serious environmental threats, and hence calls for effective analysis methods for these classes of compounds. In this study, a lab-made graphene-based solid-phase microextraction (SPME) fiber was fabricated by the sol-gel method and combined with a gas chromatography-flame photometry detector (GC-FPD) to realize the detection of trace OPPs in water samples. Compared to the commercial fiber coatings, the new sol-gel graphene fiber coatings showed advantages of good durability and solvent resistance, which were attributed to the hydrophobic and antibacterial properties of the functionalized graphene and 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (QAS). A headspace SPME method in combination with a GC-FPD was established to evaluate the performance of the novel fibers. The proposed method showed a good linear relationship for the eight OPPs (R2≥ 0.9957) in the concentration range of 1 to 1000 μg L-1, with limits of quantification of 0.11-3.37 μg L-1 and limits of detection of 0.03-1.01 μg L-1. Furthermore, the developed method also exhibited good recoveries for the analysis of OPPs both in rainwater and lake water, which demonstrates that this method is an alternative choice for multi-residue analysis of OPPs, and it has the potential for broader applications in the future.

DNA nanostructure-based drug delivery system (DDS) has become an advanced therapeutic strategy for cancer because of its unsurpassed editability, intrinsic biodegradability, and tunable multifunctionality. An intelligent DNA nanosystem integrating targeting, immunostimulation, and chemotherapy was constructed based on unmethylated cytosine-phosphate-guanine oligonucleotides (CpG ODNs) DNA nanohydrogels (CpG-MUC1-hydrogel). By facile one-step self-assembly, the cross-shaped DNAs (C-DNAs) assembled from pH-responsive I-motif sequences and targeted MUC1 aptamer-immunoadjuvant CpG-fused sequences (CpG-MUC1) were integrated into DNA nanohydrogels with controllable size by the hybridization of DNA linkers. Subsequently, DOX was successively intercalated into the base pairs of CpG-MUC1-hydrogel, resulting in CpG-MUC1-hydrogel/Dox that would disassemble and release DOX and CpGs at acidic conditions. After MUC1-mediated internalization, CpG-MUC1-hydrogel/Dox dissociated in the endo/lysosomes and induced favorable apoptosis of tumor cells. Afterward, liberated CpGs triggered vast cytokine secretion from immune cells which elicited potent immune response against malignancy. Notably, CpG-MUC1-hydrogel induced an apoptosis effect on MCF-7 cells via significantly increasing the Bax/Bcl2 ratios and a higher level of tumor necrosis factor (TNF-α) on RAW264.7 cells than naked CpGs. Our results demonstrated that self-assembled CpG-MUC1-hydrogel represented an attractive DDS for precise delivery, potent immunostimulating activity, and considerable combination efficiency with few adverse effects, which is expected to make breakthroughs in clinical translation.

A filamentary plasma jet was produced by a cylindrical dielectric-barrier discharge (DBD) equipped with a thin quartz tube. This plasma jet consists of many filaments, and the filaments bifurcate into thinner branches close to the ground electrode. Only a single filament is produced in each current pulse, and this filament is distorted in the long gas gap. The maximum electron density in the filament is on the order of $10^{15}$ cm $^{-3}$ . Optical emission examination shows a decrease of optical emissions from OH and Ar but an increase of optical emissions from N2 along the plasma jet. The vapor in the working gas argon rather than in the ambient air dominates the optical emissions from the de-excitation of OH along the plasma jet. Near the ground electrode, the nitrogen emission spectra mainly resulted from the direct electron effect on the ground state or metastable nitrogen and the collisions between nitrogen metastables. The rotational temperature is lower than the vibrational temperature but much higher than the room temperature. This feature makes the filamentary plasma jet only suitable for processing samples bearing high temperature.

An instrument combining laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy was developed for the in situ atomic and molecular composition analysis of minerals. The apparatus consist...

Label-free and in situ detection of N-glycan expression on surface of cells is vital for understanding the progression of cancer. Herein, cytosensing based on U-shaped fiber optic local surface plasmon resonance (LSPR) was developed for cancer cell detection and N-glycan evaluation on cell surface. The U-shaped fiber optic LSPR has high refractive index sensitivity (RIS). Therefore, U-shaped fiber optic LSPR cytosensing afforded ultrasensitivity for cancer cell detection with the limit of detection (LOD) of 30 cells/mL and good linearity in a wide range of 1×102-1×106 cells/mL under the optimal conditions of modified AuNPs size and Con A concentration. The U-shaped fiber optic LSPR cytosensing shows more than 29 times lower limit of detection than the straight ones. More importantly, the prepared U-shaped cytosensing was applied to evaluate the N-glycan expression level on the surface of cancer cells under different concentration external stimuli of inhibitor tunicamycin (TM). Noticeably, U-shaped fiber optic LSPR cytosensing showed an acceptable reproducibility, satisfactory anti-interference and good selectivity, and was also applied in the assessment of N-glycan expression on surface of six kinds of cell lines. Therefore, the U-shaped fiber optic LSPR offers a feasible tool in biophysical research and clinical diagnosis for cancer.

Inadequate sensitivity and side-effect are the main challenges to develop cytosensors combining with therapeutic potential simultaneously for cancer diagnosis and treatment. Herein, localized surface plasma resonance (LSPR) based on hybridized nanolayer modified Ω-shaped fiber-optic (HN/Ω-FO) was developed to integrate cytosensor and plasmonic photothermal treatment (PPT). On one hand, hybridized nanolayers improve the coverage of nanoparticles and refractive index sensitivity (RIS). Moreover, the hybridized nanoploymers of gold nanorods/gold nanoparticles (AuNRs/AuNPs) also result in intense enhancement in electronic field intensity (I). On the other hand, Ω-shaped fiber-optic (Ω-FO) led to strong bending loss in its bending part. To be specific, a majority of light escaped from fiber will interact with HN. Thus, HN/Ω-FO synergistically enhances the plasmonic, which achieved the goal of ultrasensitive cytosensor and highly-efficient plasmonic photothermal treatment (PPT). The proposed cytosensor exhibits ultrasensitivity for detection of cancer cells with a low limit of detection down to 2.6 cells/mL was realized just in 30 min. HN/Ω–FO–based LSPR exhibits unique characteristics of highly efficient, localized, and geometry-dependent heat distribution, which makes it suitable for PPT to only kill the cancer cells specifically on the surface or surrounding fiber-optic (FO) surface. Thus, HN/Ω-FO provides a new approach to couple cytosensor with PPT, indicating its great potential in clinical diagnosis and treatment.

Measurement and reconstruction of an elemental image of large brain tissue will be beneficial to the diagnosis of neurological brain diseases. Herein, laser-induced breakdown spectroscopy (LIBS) is introduced for three dimensional (3D) elemental analysis of paraffin-embedded mouse brain tissue blocks. It is used for the first time towards the mapping of mouse brain block samples. A micro-LIBS prototype is developed for brain elemental imaging and a layer-by-layer approach is used to reconstruct the 3D distribution of Ca, Mg, Na, Cu, and P in the brain tissue. Images are captured with 50 μm lateral resolution and 300 μm depth resolution. The images show that the reclamation area of the cortex surface is enriched with Ca and Mg. In contrast, the Cu distribution is circular and is found primarily in the entirety of the cerebral cortex for the paraffin-embedded brain samples. Elemental imaging results suggest that the highest P intensity is found in the cerebellum nearby the middle sagittal plane in the left-brain paraffin block. These preliminary results indicate that LIBS is a potentially powerful tool for elemental bioimaging of the whole brain and may further improve the understanding of complex brain mechanisms.

We studied the effect of optical clearing (OC) by glycerol on laser-induced tissue plasma using the immersion method. The results demonstrated the apparently enhanced effect of glycerol on the molecular spectra of the laser induced plasma. The OC is more sensitive to the molecular bands than atomic lines. After tissue immersion in the glycerol, the electron density of tissue plasma is decreased. The laser plasma temperature of the glycerol treated tissue is higher than for virgin fresh tissue. The tissue plasma after the glycerol application is still in the local thermal equilibrium plasma state. This work presents a new perspective for OC application that can extend from tissue better imaging quality to improvement of laser plasma generation.

At present, two-dimensional (2D) materials have shown great application potential in numerous fields based on their physical chemical and electronic properties. Raman spectroscopy and derivative techniques are effective tools for characterizing 2D materials. Raman spectroscopy conveys lots of knowledge on 2D materials, including layer number, doping type, strain and interlayer coupling. This review summarized advanced applications of Raman spectroscopy in 2D materials. The challenges and possible applied directions of Raman spectroscopy to 2D materials are discussed in detail.

A single-beam-splitting approach was used to enhance the signal intensity of LIBS under the extreme conditions of laser beam grazing of the surface of non-flat samples. Time-resolved spectra show that the laser-ablated plasma presents a stronger spectral intensity and a slower plasma decay in the split beam mode because of the higher laser irradiance. The temporal evolutions of signal enhancement factors indicate that the enhancement effect first rises and then drops with delay time and the maximum enhancement factor of Al plasma comes later than that of Cu plasma under the same laser energy. The mechanisms behind it are discussed. It is also found that the electron density exhibits a faster decay with delay time in the split beam mode, mainly due to the faster plasma expansion. And a slower increase of electron density with laser energy is observed in the split beam mode because of the plasma shielding effect.

In this paper, the CO2 splitting process was performed under atmospheric pressure in a multi-electrode cylindrical dielectric barrier discharge (DBD) plasma reactor. The influence of the plasma processing parameters including discharge voltage, discharge length and gas flow rate was investigated. Besides, the effect of the similar specific energy input (SEI) values obtained using different plasma powers and gas flow rates was studied. The experimental results indicated that the CO2 conversion and energy efficiency increased along with the increased discharge length due to the increased residence time and the enhanced electric field. The increase of the applied voltage and hence the plasma power or the decrease of the gas flow rate generated enhanced effect on CO2 conversion while negative influence on energy efficiency. In addition, by comparing the energy efficiency at similar SEI values obtained with different discharge powers and gas flow rates, it was found that the gas flow rate played a more important role in CO2 conversion. The proposed multi-electrode plasma reactor led to the highest CO2 conversion of 18.50% and maximum energy efficiency of 12.83%. Compared with other types of cylindrical DBD plasma reactors, the multi-electrode design proposed in this work can give a similar CO2 conversion and higher energy efficiency. The multi-electrode design can enhance the local electric field at the electrode edges, leading to the enhanced corona discharge and the generation of more micro-discharges, which is considered to be responsible for enhanced CO2 conversion process.

Laser-induced breakdown spectroscopy (LIBS) is capable of providing elemental analysis while Raman spectroscopy is powerful for molecular and structural characteristics of crystalline substances. T...

Dielectric barrier discharges (DBDs), due to its unique advantages such as simple design and low operation cost, have gained more and more attention all over the world. However, traditional plasma reactor can always have capacitive current with high peak values, which limits its further application in fields such as plasma catalytic reactions and surface treatment. In this proposed work, a new device named multielectrode cylindrical plasma reactor was presented, where the outer electrode was divided into several strips connected in parallel. The comparative electrical analysis was performed between the multielectrode plasma reactor and the traditional device. The experimental results showed that the multielectrode plasma reactor could give a much lower capacitive current peak value, namely, 5.49 mA compared with 16.26 mA of the traditional one, indicating that the new plasma reactor could decrease the capacitive current to a large extent as designed. In addition, due to the enhanced corona discharge, both the lifetime and peak values of the generated microdischarges were distributed more uniformly and concentrated in a small scale. In addition, the consumed energy by the designed multielectrode plasma reactor was decreased by 29.51% of the traditional plasma reactor, namely, 11.58 W compared with 16.43 W. The discharge mode was analyzed and determined to be mainly filament discharge with enhanced corona discharge at the electrode edges. In conclusion, the plasma reactor with proposed design can give a decreased capacitive current and also the consumed energy, which is helpful in broadening the application field of DBD in plasma catalysis fields.

Developing cost‐efficient large‐scale uniform plasma jets represents a significant challenge for high performance in material processing and plasma medicine. Here, a V–I characteristic modulation approach is proposed to reduce the discharge power and increase the plasma scale and chemical activity in non‐self‐sustained atmospheric direct‐current discharges. The electric field in discharge space is optimized to fundamentally empower simultaneously initiating all discharge cells far below Townsend breakdown potential and stably sustaining each plasma jet at low voltage. These strategies create a crucial step to fabricating a flexible and compact low‐power large‐scale uniform laminar plasma jet array (LPJA) with high activity in cheap argon. The mechanisms behind the discharge enhancement are revealed by combining V–I characteristic examination and a modulation model. Compared with conventional arrays, this LPJA possesses the widest size (90 mm) and raises its uniformity from 30% to 97%. Comparing different discharge modes shows that the LPJA scale is surprisingly increased nearly by 4 times with the discharge power reduced from 7.4 to 4.8 W. The methodology provides a highly cost‐efficient roadmap to break through the bottleneck of restricting low‐power discharge, large‐gap discharge, large‐scale discharge, parallel‐multi‐electrode discharge, and uniform discharge together. This advance will meet the urgent need for various plasma applications., A V–I characteristic modulation approach is proposed in non‐self‐sustained direct‐current discharge to greatly reduce the discharge power and largely increase the plasma scale and chemical activity. In conjunction with the electric field optimization to realize the discharge simultaneity and stability, a highly cost‐efficient large‐scale uniform laminar plasma jet array is fabricated for material processing and plasma medicine.

As a potential technology, the plasma-based conversion of CO2 comes under the spotlight. The microwave plasma stands out, owing to the high-degree of non-equilibrium that is desired by the vibrational excitation of CO2. This paper is an overview of recent studies to illustrate the state of CO2 conversion in microwave plasma. In this paper, interactions between the CO2 dissociation and operating conditions, such as input power, pressure, temperature, and gas flow, were comprehensively discussed based on a deep understanding of the reaction mechanism. The conversion of CO2 and co-reactants, which makes a difference to the CO2 conversion and production of high value-added compounds, was analyzed and followed with the implementation of catalysts. To sum up, we discussed the prospects and remaining challenges for the further development of CO2 conversion in microwave plasma.

Aiming to decrease the dielectric barrier discharge (DBD) capacitive current, a new type of multi-electrode cylindrical DBD plasma reactor was proposed in this work. Due to the novel multi-electrode design, the discharge current peak value of the newly designed plasma reactor decreased by 66.24%, from 16.26 mA for the traditional device to 5.49 mA. Besides, the number of the micro-discharges was found almost 2 times higher than that of the traditional device, indicating the generating of more discharge channels (from 37 to 89). The enhanced corona discharge formed at the electrode edges caused by fringe effect was considered as the main reason. The opti-electrical analysis was performed using multi-electrode plasma reactors with different electrode configurations. The changes of optical emission efficiency (Ieff), equivalent capacitance of dielectric layer (Cd) and the discharge gap (Cg) were investigated under different applied voltage, discharge length, interval between adjacent outer electrodes and electrode width. The experimental results indicated the efficient discharge length l and fringe effect were responsible for the variations of Ieff, Cd and Cg. Higher applied voltage resulted in a higher Ieff, but higher current at the same time. Besides, Cd gradually increased along with the increased applied voltage while Cg presented the decreased trend. Ieff increased along with the enhanced fringe effect caused by the shorter electrode width and smaller interval between adjacent outer electrodes, while decreased with the increased discharge length. Cd and Cg decreased with increased interval between outer electrodes, but increased with the enhanced discharge length and electrode width. The voltage distribution analysis indicated that the change of Ieff was mainly due to the change of the voltage across the gas gap Vg. This work can give a deeper and further understanding on the discharge characteristics of the proposed multi-electrode plasma reactor.

In this work, we report a low-cost and easy operation biosensor platform capable of detection of various analytes with high sensitivity and good selectivity. By ingeniously assigning the specific aptamer into a primer-template integrated DNA template, and using monolayer graphene oxide as a reversible and nonspecific inhibitor, the simple biosensor platform is set up. Without a target, the DNA template is constrained by the graphene oxide sheet and results in low signal. In the presence of a target, the constrained DNA template is released from the graphene oxide surface via a target-induced aptamer conformational change, and further amplified through the improved strand displacement amplification reaction. Therefore, the target detection is simply converted to DNA detection, and a correlation between target concentration and fluorescence signal can be set up. As a result, dozens-fold signal enhancement, high sensitivity, good selectivity, and potential practicability are achieved in target detection. More importantly, the proposed biosensor platform is versatile, meaning that it can greatly facilitate the detection of a variety of analytes. Due to the low cost and easy availability of sensing materials, and the elimination of tedious detection operations, we believe that this simple and universal biosensor platform can find wide applications in biological assay and environment monitoring.

In this work, a compact laser induced breakdown spectroscopy (LIBS) instrument was developed based on a high energy lightweight laser source and an integrated control system, making the instrument ...

Combustion provides about 80% energy for our daily life and industrial production. But thermal efficiency of traditional combustion technologies is low, which causes energy waste and serious environmental pollution. In order to improve the combustion efficiency, a combined method based on non-equilibrium plasma generated by dielectric barrier discharge and OH radicals coming from water-steam additive was proposed in this work, and plasma assisted propane combustion was examined and evaluated. The results indicated that when relative humidity (RH) was 20% and applied peak voltage was fixed at 8.75 kV, the relative intensity of OH radical and the flame temperature reached the maximum value at the flame root. At the same time, propane combustion was the most complete. In addition, we found that the erosion of the inner electrode was weakened by H2O addition, and the symmetry of discharge current was changed from symmetry to asymmetry with the increase of RH. Compared with the pure air undischarged combustion, when the relative humidity was 20% and under the discharge conditions of 8.75 kV, the lean-burn extinction limit was extended to 0.4,which is far lower than the traditional lean-burn limit (0.51).

The development of a universal, sensitive, and rapid assay platform to achieve detections of heavy metal, nucleic acid and bacteria is of great significance but it also faces a thorny challenge. Herein, a novel and universal array platform was developed by combining photonic crystals (PCs) and DNA nanomachine. The developed array platform integrated the physical and biological signal amplification ability of PCs and DNA nanomachine, resulting in ultrasensitive detections of Hg2+, DNA, and Shigella sonnei with limits of detection (LODs) of 22.1 ppt, 31.6 fM, and 9 CFU/mL, respectively. More importantly, by utilizing a microplate reader as signal output device, the array achieved high-throughput scanning (96 samples/3 min) with only 2 μL loading sample, which is advantageous for the detection of infectious dangerous targets. In addition, the PCs array could be obtained easily and rapidly based on self-assembly of colloidal nanospheres, and the DNA nanomachine was operated with enzyme-free and time-saving features. Benefiting from these merits, the proposed PCs array offered a powerful universal platform for large-scale detection of various analytes in the fields of pollution monitoring, epidemic control, and public health.

The prevalent catalysts for natural and artificial N2 fixation are known to hinge upon transition-metal (TM) elements. Herein, we demonstrate by density functional theory that Al-doped graphene is a potential non-TM catalyst to convert N2 to NH3 in the presence of relatively mild proton/electron sources. In the integrated structure of the catalyst, the Al atom serves as a binding site and catalytic center while the graphene framework serves as an electron buffer during the successive proton/electron additions to N2 and its various downstream NxHy intermediates. The initial hydrogenation of N2 can readily take place via an internal H-transfer process with the assistance of a Li+ ion as an additive. In view of the recurrence of H transfer in the first step of N2 reduction observed in biological nitrogenases and other synthetic catalysts, this finding highlights the significance of heteroatom-assisted H transfer in the design of synthetic catalysts for N2 fixation.

Sample introduction has always been a significant issue in the research of plasma emission spectrometry. In this paper, the continuous direct solid sampling (CDSS) technique, a novel and alternative technique for direct solid analysis based on microwave plasma atomic emission spectrometry (MWP-AES), was firstly proposed. By allowing the plasma column to directly interact with the solid sample surface, the sample was heated and melted, and the elements in the sample were atomized and excited continuously. With the help of multivariate analysis, elements including Corg, Cu, Pb and Cr in geological samples were qualitatively and quantitatively determined. To construct a robust and accurate support vector regression (SVR) model, spectral bands consisting of characteristic lines and adjacent noise zones were selected as input variables. The penalty parameter C and the key parameter of the radial basis function (RBF) were optimized to be 16.0453 and 2.9008, respectively. The optimized model showed satisfactory results with a linearity correlation coefficient R2 better than 0.99 and RSD lower than 11.08% for all target elements. The proposed CDSS technique can be used to successfully conduct direct solid analysis, avoiding the use of chemical reagents, which makes it green and environmentally friendly. The total analysis time can cost less than half a minute, indicating that the proposed method can be promising in high throughput and rapid analysis. What is more, the CDSS technique combines sampling, atomization and excitation together, which eliminates the use of an electrothermal vaporization or laser ablation unit when analyzing solid samples directly using MWP-AES. The proposed method opens a promising and alternative door for plasma spectrometry especially for MWP-AES due to the advantages of continuous direct solid analysis, rapid analysis speed, no or minimal sample pretreatment, and a simplified analytical system, which is suitable for in situ and field analysis.

We fabricate a high-efficient ion source for real time on-line monitoring of trace compounds in ambient air by introducing a weak longitudinal magnetic field to a micro-fabricated DC glow discharge. Mass spectrometric detection of various samples indicates that the signal intensity increases by an order of magnitude and the limit of detection can be lowered to 1/10 of the original level. This improvement results from the increasing ion transport efficiency through the magnetic confinement.

Due to the widespread use of tetracycline (TC), there is an increasing demand for rapid detection as well as effective removal of residual tetracycline for environment and food safety. Herein, we report an Eu/Zr-MOF material that combines the high adsorption performance of water-stable Zr-MOF and the unique emission characteristics of Eu3+, which enables both sensing and adsorption functions for TC. Eu/Zr-MOF can be achieved facilely by doping Eu3+ into Zr-MOF via the traditional hydrothermal method. In aqueous medium, the Eu3+ preferentially coordinate with TC molecules, which in turn acts as an antenna for UV–Vis absorbance to enhance the characteristic fluorescence of Eu3+. In such way, TC can be specifically detected in a wide dynamic range (0.001–0.5 µg/mL) with a low detection limit (0.00092 µg/mL). Moreover, by taking advantage of the unsaturated character of Zr O centers, the Eu/Zr-MOF has a TC loading capacity as high as 289 mg g-1. As a consequence, based on the Eu/Zr-MOF, rapid detection and efficient removal of TC from food and environment was realized at once. The principle of design proposed in this work may find more applications to synthesize new platforms for simultaneous sensing and removal of specific pollutants.

A newly designed and developed bench-top instrument is reported for laser-induced breakdown spectroscopy offering compact size and relatively low cost. A miniature laser was designed in the laboratory with a small volume and a light weight. The spectrometer was controlled using laboratory-written software. The instrument is suitable for the direct and rapid analysis of solid samples after simple pretreatment. Good stability and accuracy were achieved for quantitative analysis. The performance of the instrument was evaluated by qualitative and quantitative analyses of nickel ore for Mn, Al, Fe, Cr, Zn, Mg, Si, and Ca. The quantitative analysis showed linear calibration graphs and small relative standard deviations. The results show that the new instrument is suitable for elemental analysis.

Three-dimensional nano-biointerfaces, emerging as significant cell-guiding platforms, have attracted great attention. Nevertheless, complicated chemical modifications and instability of bio-ligands limit their widespread application. In this study, a novel biointerface, based on silicon nanowires (SiNWs) array, was prepared for bacterial capture and sensing. Vertically aligned SiNWs were fabricated via metal assisted chemical etching and decorated with uniform Au@Ag core-shell nanoparticles (Au@Ag NPs). These deposited Au@Ag NPs formed multi-scale topographic structures with nanowires, which provided effective attachment sites for bacterial adhesins. In addition, the Au cores of Au@Ag NPs enhanced the activity of the surface silver atoms and promoted the binding of Au@Ag NPs to bacteria. Thus, the Au@Ag NPs decorated SiNWs (SiNWs-Au@Ag) substrate exhibited high capture capacity for bacteria in drinking water (8.6 and 5.5 × 106 cells per cm2 for E. coli and S. aureus in 40 min, respectively) via physical and chemical effects. Bacteria in drinking water can be sensitively detected by using a combination of laser induced breakdown spectroscopy (LIBS) and label based surface-enhanced Raman spectroscopy (SERS) techniques. Due to the antibacterial activity of Au@Ag NPs and the physical stress exerted on SiNWs, the prepared biointerface also showed high antibacterial rates towards both Gram-positive and Gram-negative bacteria strains. With these excellent properties, the flexible sensing platform might open a new avenue for the prevention and control of microbial hazards in water.

The characteristics of the dielectric barrier discharge (DBD) equipped with asymmetrical electrode (ring electrode on the upper and disk electrode on the lower) in atmospheric helium are investigated by a two-dimensional self-consistent fluid model. Simulation results show that as the applied voltage increases, the discharge enhances and the onset of discharge advances, which is similar to the results of traditional DBD. However, with the applied voltage increasing, the symmetry of the discharge current pulses in the positive and negative half cycles disappears because of the asymmetric electrode configuration. In addition, only the spatial distribution of the electron density at the peak moments of the first and second current pulses satisfies the complementary characteristics, while the spatial distribution at other peak moments does not meet the complementary characteristics. Moreover, the electric field, near the upper dielectric barrier surface, presents a curtain-like distribution with considerable radial electric field components, which results from the non-uniform radial surface charge distribution and the ring electrode configuration. The relative variation of the radial distribution of surface charge density is largely determined by the geometry of the opposite electrode.

Laser-induced breakdown spectroscopy (LIBS) is becoming a rapid and easy technique for quantitative elemental analysis. However, the implementation of accurate quantitative LIBS analysis is always subject to noise interference. In this work, in order to improve LIBS analysis performance for trace elements in aluminium alloys, a modified trade-off soft and hard threshold method is proposed based on the wavelet theory, where optimal parameters are deduced to eliminate noise interference. By using the modified algorithm combined with an Al I line at 308.215 nm as an internal standard, the statistical parameters including the determination coefficient (R2), the root mean square error (RMSE) and the relative standard deviation (RSD) of magnesium (Mg), manganese (Mn) and cuprum (Cu) in aluminium alloys are all significantly improved. The most significant improvement of R2 is 0.066 for Cu. The maximum RMSE reduction value is 0.583 for Mg, and the mean value of RMSE reduction is 0.261 for all three trace elements. And after de-noising, the value of RSD gets smaller for each trace element. Such results indicate that the optimized algorithm is valid for the effective improvement of the accuracy of quantitative LIBS analysis in the trace element determination of aluminium alloys.

Laser-induced breakdown spectroscopy (LIBS) is a simple, fast, and direct technique for the elemental analysis of various samples. However, the practical application of this method in direct liquid analysis is limited due to its inherent disadvantages including surface ripples and extinction of emitted intensity. Applicable treatments of liquids always involve complicated procedures or additional instruments, which is disadvantageous to its analytical performance. In this study, we proposed a novel method for the LIBS analysis of liquid samples via a hydrogel-based solidification technique. In this new method, aqueous solution is directly poured into sodium polyacrylate resins. Owing to the high hydroscopicity of sodium polyacrylate resins, the resins quickly form a hydrogel and immediately solidify the liquid samples. After this, the LIBS analysis is directly performed. To estimate the analytical performance of this proposed method, calibration curves were established and limits of detection for Al, Cu, and Cr were obtained. The limits of detection (LODs) for the emission lines of Al(I) 308.21 nm, Cu(I) 324.75 nm, and Cr(I) 425.43 nm were 0.460 μg mL−1, 4.69 μg mL−1, and 4.44 μg mL−1, respectively. According to the obtained results, this proposed method demonstrates its better analytical performance in terms of LODs at the ppm level and requires shorter processing time as compared to other analytical methods based on the LIBS technique for liquid sample analysis. Especially, the short pretreatment of samples and simple auxiliary equipment make this hydrogel-based solidification method bring LIBS out of the laboratory for the direct analysis of environmental liquid samples. The feasibility and potential of this novel method have also been discussed for special analytical applications in slurry samples.

A 1-D self-consistent fluid model was employed to investigate the effect of driving frequency on the discharge characters of a dielectric barrier discharge at atmospheric pressure in argon excited by a periodic Gaussian voltage. The simulation results indicate that there are two discharge modes: 1) Townsend and 2) glow modes in the multipulse discharge and different transitions between them during the discharge take place with the increase in driving frequency. When the driving frequency is 1 kHz, there is a tendency of transition from the Townsend mode through glow and finally back to the Townsend one during the positive half-circle of applied Gaussian voltage. However, the discharge in the half-circle can all along operate in the glow mode with the higher driving frequency. Moreover, when the driving frequency is sufficiently high, there are also distinct fluctuations of spatial performance of the charge densities in the positive column during the glow discharge. This is caused by the fact that a lot of charged particles created in the gas gap have not enough time to drift and diffuse to the dielectric barriers, and then these particles are preserved in the local discharge gap at such a high frequency. A comparison of the spatial and temporal evolutions of the electron density at different driving frequencies indicates that the increase in the driving frequency can enhance the plasma chemistry and also expand its volume.

Optical emission of laser ablation plasma on a shale target surface provides sensitive laser-induced breakdown spectrometry (LIBS) detection of major, minor or trace elements. An exploratory study for the characterization of the plasma induced on shale materials was carried out with the aim to trigger a crucial step towards the quantitative LIBS measurement. In this work, the experimental strategies that optimize the plasma generation on a pressed shale pellet surface are presented. The temporal evolution properties of the plasma induced by ns Nd:YAG laser pulse at the fundamental wavelength in air were investigated using time-resolved space-integrated optical emission spectroscopy. The electron density as well as the temperatures of the plasma were diagnosed as functions of the decay time for the bulk plasma analysis. In particular, the values of time-resolved atomic and ionic temperatures of shale elements, such as Fe, Mg, Ca, and Ti, were extracted from the well-known Boltzmann or Saha–Boltzmann plot method. Further comparison of these temperatures validated the local thermodynamic equilibrium (LTE) within specific interval of the delay time. In addition, the temporal behaviors of the signal-to-noise ratio of shale elements, including Si, Al, Fe, Ca, Mg, Ba, Li, Ti, K, Na, Sr, V, Cr, and Ni, revealed the coincidence of their maximum values with LIBS LTE condition in the time frame, providing practical implications for an optimized LIBS detection of shale elements. Analytical performance of LIBS was further evaluated with the linear calibration procedure for the most concerned trace elements of Sr, V, Cr, and Ni present in different shales. Their limits of detection obtained are elementally dependent and can be lower than tens of parts per million with the present LIBS experimental configurations. However, the occurrence of saturation effect for the calibration curve is still observable with the increasing trace element content, indicating that, due to the complex composition of shale materials, the omnipresent “matrix effect” is still a great challenging for the performance of quantitative LIBS measurement even in the framework of the LTE approach.

Laser-induced breakdown spectroscopy, coupled with advanced chemometric methods, was used to quantitate multiple elements in a seaweed-based fertilizer. The influence of important parameters was determined using partial least squares regression (PLSR), support vector regression (SVR) and random forest (RF) optimizations. Optimal results for Mg, K and P were obtained using PLSR, whereas RF yielded the best results for Mn, Cu, Sr and Ca. The best predictions for Ba levels were obtained with SVR. The lowest root mean square errors in the prediction sets for Mn, Cu, Sr, Ba, Mg, K, P and Ca were 48.27 µg/g, 36.90 µg/g, 0.37 mg/g, 40.32 µg/g, 1.99 mg/g, 2.03 mg/g, 4.81 mg/g and 14.08 mg/g, respectively, with average relative standard deviations of 13.65%, 2.68%, 19.80%, 5.17%, 3.32%, 2.98%, 1.82% and 5.81%. The results showed that the optimal multivariate model depended on the specific element being analyzed. The proposed method provides a rapid means of determining multielement concentrations in seaweed-based fertilizers.

A novel and simple experimental system was designed in the present work for real-time particle analysis using a laser-induced breakdown spectroscopy (LIBS) technique without time-consuming pretreatment processes, which can also effectively avoid inherent difficulties such as particle splashing during the particle LIBS analysis. In addition, the advantages of this novel and simple experimental system, including being simple and fast, are in conformity with the characteristics of the LIBS technique. In this study, Geochemical Standard Reference Soil particles were selected as the samples for demonstrating the novel analytical method. The soil samples were transferred to an adsorption plate via argon gas and the adsorption plate was placed on a two-dimensional rotating stage. Owning to good stickiness, the adsorption plate can hold a large number of particle samples, and the rotating stage ensures that each laser pulse shoots on a fresh target surface, which can effectively improve the accuracy during the LIBS analysis. To verify this novel analytical method, the calibration curves for titanium (Ti) and magnesium (Mg) were obtained. Under the optimized conditions, the limits of detection (LOD) for Ti and Mg in soil samples using this system are 124.571 μg g−1 and 0.0126%, respectively. The results show that the novel method designed in the present study is a feasible option for analyzing metallic elements in particle samples using the LIBS technique and could have potential applications for practical and online analysis.

A novel method with high sensitivity was developed for determining ultra-trace-amounts of metallic elements in liquids by LIBS analysis, based on crosslinked polyvinyl alcohol (PVA) supporting material. In this newly proposed approach, an aqueous solution sample was intensively mixed with PVA solution leading to phase conversion, which is distinguished from the desiccation process on a solid supporter as reported in the literature of liquid-to-solid conversion for LIBS analysis. The analytes were distributed in a thin PVA film (0.34 mm) as a result of crosslinking the polymer materials, and thereby the plasma signals generated by laser pulse were stronger and a lower amount of solid supporter was needed compared to traditional methods. Due to the low PVA thermal decomposition temperature, laser generated plasma energy was effectively utilized for not only ablating the sample, but rather exciting analytes within the sample. The limits of detection for Ag, Cu, Cr, Pb, Ni, Co and Cd obtained in this study were 1 ng mL−1, 8 ng mL−1, 16 ng mL−1, 1 μg mL−1, 1 μg mL−1, 2 μg mL−1 and 5 μg mL−1, respectively, which showed great improvement compared with those from direct liquid analysis by LIBS. The satisfactory figures of merits of the proposed method, including linearity, reproducibility and accuracy, were also obtained with the optimal experimental parameters. This unique method takes advantage of mixing an aqueous solution sample with supporter material in a liquid phase and it has characteristics of fast, simple and sensitive analysis for liquid sample compared with conventional liquid-to-solid conversion methods for LIBS.

Gas shale is one of the important unconventional hydrocarbon source rocks, whose composition, such as mineral components and redox sensitive trace elements, has been proved as important geochemical proxies playing essential roles in indicating the gas potential and gas productivity in recent geological researches. Fast and accurate measurements for the shale composition, especially those with spatial resolution, will reveal rich information for the understanding and evaluation of gas shale reservoirs. In this paper, we demonstrated the potentiality as well as feasibility of laser-induced breakdown spectroscopy as an effective technique to perform spectrochemical analysis for shale samples. In case of the bulk analysis of pressed shale pellet, spectral analysis of the plasma emission revealed high sensitivity of LIBS for major, minor and even trace elements. More than 356 lines emitted by 19 different elements can be found. Among these species, redox sensitive trace elements such as V, Cr, and Ni were detected with high signal-to-ratios. Two-dimensional surface micro-analysis for the concerned major or minor elements with strong emissions was then applied to the smoothed shale slab. Local thermodynamic equilibrium for the plasma was first verified with a line profile point-by-point on the sample surface, the matrix effect was then assessed as negligible by the extracted electron density and temperature of the plasmas induced at each position on the same profile. Concentration mappings for the major elements of Si, Al, Fe, Ca, Mg, Na and K were finally constructed with their measured relative variations of line emission intensities. The distribution and correlations of these elements in concentration may reflect changes of shale mineral components with respected to the variations of the depositional environments and provide an important clue in identifying sedimentary processes when combined with other geological or geochemical evidences. These results well demonstrated the potential of LIBS technique for shale studies.

Fiber optic-based biosensors with surface plasmon resonance (SPR) technology are advanced label-free optical biosensing methods. They have brought tremendous progress in the sensing of various chemical and biological species. This review summarizes four sensing configurations (prism, grating, waveguide, and fiber optic) with two ways, attenuated total reflection (ATR) and diffraction, to excite the surface plasmons. Meanwhile, the designs of different probes (U-bent, tapered, and other probes) are also described. Finally, four major types of biosensors, immunosensor, DNA biosensor, enzyme biosensor, and living cell biosensor, are discussed in detail for their sensing principles and applications. Future prospects of fiber optic-based SPR sensor technology are discussed.

A facile and green method was employed to synthesize the tannic acid functionalized graphene nanocomposite (TA-G) using tannic acid as reducing as well as capping reagent which could alter graphene surface physicochemical properties to improve the adsorption efficiency. Then the as-prepared TA-G was used as adsorbent to investigate the adsorption behavior for rhodamine B (RB). Due to the intensive π–π stacking interaction and electrostatic attraction, TA-G exhibited fine adsorption performance for RB. The adsorption isotherm fitted Langmuir model well and the theoretical maximum of adsorption capacity calculated by Langmuir model was 201 mg g−1 which was approximately in a close agreement with the experimental measured data. The kinetics of adsorption was consistent with the pseudo-second-order model perfectly and chemisorption was the speed limit step. Therefore, the as-prepared TA-G nanocomposite would be an ideal adsorbent for the removal of RB in aqueous solution and opened a new door to broaden the potential applications of graphene in environmental research.

CdS quantum dot (QD) is a typical kind of II-IV nanoparticles, which plays an important role in the common type of core-shell QDs. It is of great practical significance to synthesize the water-soluble CdS QDs used in multicolor biomarkers and prepare core-shell QDs. In our case, we came up with a novel green method to manufacture CdS QDs with high quality, different size, and adopted UV-vis absorption, fluorescence, FTIR, XPS, HRTEM, SAED and STEM-EDX to discuss their growth mechanism. We successfully constructed fluorescence resonance energy transfer (FRET) system between CdS QDs and gold nanoparticles (AuNPs), then comprehensively and systematically studied the interaction between them.

Laser-induced breakdown spectroscopy (LIBS) integrated with random forest (RF) was developed and applied to the identification and discrimination of ten iron ore grades. The classification and recognition of the iron ore grade were completed using their chemical properties and compositions. In addition, two parameters of the RF were optimized using out-of-bag (OOB) estimation. Finally, support vector machines (SVMs) and RF machine learning methods were evaluated comparatively on their ability to predict unknown iron ore samples using models constructed from a predetermined training set. Although results show that the prediction accuracies of SVM and RF models were acceptable, RF exhibited better predictions of classification. The study presented here demonstrates that LIBS–RF is a useful technique for the identification and discrimination of iron ore samples, and is promising for automatic real-time, fast, reliable, and robust measurements.

A highly concentrated, ring-shaped phase conversion (RSPC) method was developed for liquid sample analysis using the laser-induced breakdown spectroscopy (LIBS) technique. In this work, test samples were prepared by mixing the metal particles with polyvinyl alcohol (PVA) supporter in liquid phase. With heat, the PVA solution solidified inside a modified glass petri dish, forming a metal-enriched polymer ring film. Distinguished from other traditional liquid-to-solid conversing methods, the proposed new method takes advantage of enhanced homogeneity for the target elements inside the ring film. The modified glass petri dish was used to control the ring-shaped concentration. Due to the specially designed circular groove at the bottom of this dish, where the PVA solution and liquid sample mixture accumulated, the target elements were concentrated in this small ring, which is beneficial for enhancing and stabilizing the plasma signals compared to the direct liquid sample analysis using LIBS. The limits of detection for Ag, Cu, Cr, and Ba obtained with the RSPC-LIBS technology were 0.098 μg·mL-1, 0.18 μg·mL-1, 0.83 μg·mL-1, and 0.046 μg·mL-1, respectively, which provided greater improvement than the direct bulk liquid analysis using LIBS.

This work demonstrates the application of a novel microwave induced plasma ionization (MIPI) source to ion mobility spectrometry (IMS). The MIPI source, called Surfatron, is composed of a copper cavity and a hollow quartz discharge tube. The ion mobility spectrum of synthetics air has a main peak with reduced mobility of 2.14 cm2V−1s−1 for positive ion mode and 2.29 cm2V−1s−1 for negative ion mode. The relative standard deviations (RSD) are 0.7% and 1.2% for positive and negative ion mode, respectively. The total ion current measured was more than 3.5 nA, which is much higher than that of the conventional 63Ni source. This indicates that a better signal-to-noise ratio (SNR) can be acquired from the MIPI source. The SNR was 110 in the analysis of 500 pptv methyl tert-butyl ether (MTBE), resulting in the limit of detection (SNR = 3) of 14 pptv. The linear range covers close to 2.5 orders of magnitude in the detection of triethylamine with a concentration range from 500 pptv to 80 ppbv. Finally, this new MIPI-IMS was used to detect some volatile organic compounds, which demonstrated that the MIPI-IMS has great potential in monitoring pollutants in air.