In order to obtain a stable plasma and improve the performance of the torch for atomic emission spectroscopy( AES), the structure of microwave plasma torch(MPT) was analyzed. The transmission and distribution characteristics of the electromagnetic field of the torch configuration with two or three concentric tubes, as well as the metal spacer between inner and intermediate tubes with different depths were simulated with electromagnetic simulation software and verified by experiments. The results indicate that the inner tube of MPT plays an important role in strengthening the electric field intensity at the opening end of the MPT and redistributing the electromagnetic field in the whole torch by forming a double resonance configuration, and contributes to enhancing the macroscopic stability and the self-sustainment of the plasma. The stability of the plasma is proved to be excellent when the metal spacer between the inner and intermediate tubes is located at a place 20—30 mm away from the top opening of the torch. A proper location of the spacer can also avoid the formation of a static filament plasma or a rotating plasma rooted from the outer wall of the inner tube. With the help of morphological analysis, the underlying reason why MPT possesses a great tolerance to wet aerosols and air introduction was clearly made, that is, the formation region of the plasma formed with MPT is apparently separated from the reaction zone of it.

A nanoliter self-priming compartmentalization (SPC) microfluidic chip suited for the digital polymerase chain reaction (dPCR) analysis in point-of-care testing (POCT) has been developed. This dPCR chip is fabricated of polydimethylsiloxane (PDMS). After the dPCR chip is evacuated, there will be a negative pressure environment in the chip because of the gas solubility of PDMS. The negative pressure environment can provide a self-priming power so that the sample solutions can be sucked into each reaction chamber sequentially. The whole sampling process requires no external power and is valve-free. Channels that contain water are designed around each sample panel to prevent the solvent (water) from evaporating during dPCR process. A glass coverslip is also used as a waterproof layer, which is more convenient and more efficient than other waterproof methods seen in literature. This dPCR chip allows three samples to be amplified at the same time. Each sample is distributed into 1040 reaction chambers, and each chamber is only 2.08 nL. Human β-actin DNA solutions of known concentrations are used as the templates for the dPCR analyses to verify the sensitivity and accuracy of the method. Template DNA solutions diluted to concentrations of 300, 100 and 10 copies/μL are tested and shown that this simple, portable and self-priming dPCR chip can be used at any clinic as a real POCT technique.

The fast, sensitive detection for 6 aromatic amines and direct observation of intermediates of Schiff-base reactions were achieved through reactive desorption electrospray ionization mass spectrometry (reactive DESI-MS). Pure acetone was electrosprayed to impact the aromatic amines on the paper, allowing two reactions, a proton-transfer reaction and a Schiff-base reaction, to occur in these experiments. The former was used to detect the aromatic amines, and the protonated analytes generated were selected for the qualitative and quantitative analysis. The false-positive signals were excluded by tandem mass spectrometry. For the 6 analytes, linear signal responses were obtained, and each had a dynamic range of 5 orders of magnitude. The relative standard deviation (RSD) and limit of detection (LOD) for all the measurements were in 1.5–5.3% and 0.03–0.2 pg/mm2 range, respectively. The latter is a nucleophilic addition reaction that occurred between the aromatic amines and the acetone. The carbinolamine intermediates of these reactions were directly detected and identified by reactive DESI-MS. The data show that reactive DESI-MS is not only a reliable, sensitive tool for chemical analysis, but also a valid and promising method for studying organic reactions simultaneously, especially for heterogeneous reactions that occurred at a solution/solid interface.Highlights► 6 suspected carcinogenic aromatic amines were qualitatively and quantitatively analyzed without sample pretreatment. ► The intermediates of the heterogeneous Schiff-base reactions were directly observed and identified. ► Acetone was verified to be another choice of the spray solvent of DESI-MS.

We have developed a rapid, simple and label-free colorimetric method for the identification of target DNA. It is based on loop-mediated isothermal amplification(LAMP). Plain gold nanoparticles(AuNPs) are used to indicate the occurrence of LAMP. The amplified product is mixed with AuNPs in an optimized ratio, at which the deoxyribonucleotides( dNTPs) bind to the AuNPs via ligand-metal interactions and thus enhance AuNPs stability. If a target DNA is amplified, the dramatic reduction of the dNTPs leads to the aggregation of AuNPs and a color change from red to blue. The success of the method strongly depends on the ionic strength of the solution and the initial concentration of dNTPs. Unlike other methods for the identification of isothermal products, this method is simple and can be readily applied on site where instrumentation is inadequate or even lacking.

•The system comprises a transition channel that is used for fluid acceleration.•The system could provide sufficient biosample volume.•The system could provide a relatively stable flow rate.•The system is tubeless and needs no external control.A number of portable surface plasmon resonance (SPR) devices have been developed for point-of-care (POC) testing. Meanwhile, micropumps have been fabricated to be integrated into these devices for flow injection analysis (FIA). However, the (micro) pumps, the tubes and their external control units were space-consuming. Here we developed a power-free flow injection analysis (FIA) method for SPR detection based on a gravity-induced flow injection (gFI) system. The gFI system was tubeless and did not need to be controlled. The fluid was driven into the detection areas by its own gravitational force. A transition channel was used to increase the liquid-level difference between the inlet reservoir and the outlet reservoir. After a liquid sample was placed in the inlet reservoir, the flow rate of the liquid sample was increased in the transition channel. Before it arrived at the sensing surface, the flow rate of the sample was steady (with an error of less than 10%). The fluctuation of the flow rate had an influence on the SPR response signal, which was successfully denoised using an internal reference. With the gFI system, the SPR imaging biosensor was able to perform real-time detection manually. The SPR responses of DNA hybridization and protein immobilization were successfully obtained.

We report here a label-free method for ultrasensitive and selective assay of protease activity based on the peptide-induced fluorescence quenching of conjugated polyelectrolyte (PPESO3). It is very interesting to find that there is a critical length of oligo-polyarginine (i.e., Arg5) below which 1) the quenching efficiency of PPESO3 is sharply decreased, and more importantly, 2) the trypsin-catalyzed hydrolysis is greatly slowed down. This opens good opportunities for not only the ultrasensitive assay of trypsin, but the specific detection of other proteases if carefully designing an appropriate peptide length and the cleavage site. Herein, the enzyme selected as a proof of concept is chymotrypsin. Due to the essence that any cleavage of the designed peptide probes will result in a notable decrease or even a complete loss of their capability to quench the emission of PPESO3, the limits of detection for trypsin and chymotrypsin have been found as low as 0.25 ng/mL (11 pM) and 0.15 ng/mL (6 pM), respectively. Both are superior to those of most previous methods by 1–2 orders or higher.Highlights► A label-free, ultrasensitive and selective assay of protease activity is developed. ► A critical peptide length for PPESO3 quenching and trypsin digestion is demonstrated. ► Proper length of oligo-polyarginine ensures the most efficient fluorescence turn-on. ► Critical peptide length for trypsin digestion enables specific assay of chymotrypsin. ► Detection limit for trypsin and chymotrypsin are as low as 11 and 6 pM, respectively.

The aqueous CdTe quantum dots (QDs) were synthesized by the electrostatic reaction method. The optical properties of CdTe QDs were investigated by femtosecond Z-scan and time-resolved luminescence technique in nonresonant spectral region. The nonlinear absorption and refraction are ascribed to two-photon absorption, and time-resolved upconversion photoluminescence produces biexponential decay pattern at infrared femtosecond laser excitation. Upconversion luminescence is composed of a band-edge excitonic state and a photoinduced trapping state. The short-lived band-edge excitonic emission is independent of the detection wavelengths, and long-lived species becomes even longer with the increase of detection wavelengths, which indicates the size dependence of surface excitonic emission.