Ultrafast and field-based detection of methamphetamine in hair with Au nanocake-enhanced Raman spectroscopy.

The disaster and devastation from abuse of Methamphetamine (MAMP) have a serious impact on people's mental and physical health. Developing a rapid and accurate method to screen drug suspects and thus control MAMP abuse is essential to social security. Hair analysis for MAMP detection is considered to be one of the most potential methods for monitoring drug abuse due to its convenient sample collection, easy for storage and long traceability period. However, the current accurate detection of MAMP in hair primarily utilizes hyphenated mass spectrometry (MS) techniques, but it is not suitable for field-based detection due to the bulky instrument. Hence, developing alternative portable detection techniques for rapid on-site detection of MAMP in hair is an urgent problem to be solved. Here, the high-performance Au nanocakes (Au NCs) were constructed as surface-enhanced Raman spectroscopy (SERS) substrates to detect MAMP in hair, realizing 5 min ultrafast and ultrasensitive detection utilizing a portable Raman spectrometer. Experiments and finite-difference time-domain (FDTD) simulations show that Au NCs have stronger enhancement than Au nanospheres (Au NPs), and 0.5 ppb (3.35 × 10-9 M) MAMP standard is stably detected by Au NCs as an enhanced substrate. A strategy of liquid-liquid microextraction was exploited to eliminate the interference of complex matrices in hair. This method exhibited excellent reproducibility and temporal stability across different drug addicts (relative standard deviation was 5.14% within 160 s). Our approach shows great promise in public safety, providing a rapid and accurate method to detect in hair by SERS.

Electric field assisted surface plasmon-coupled directional emission: an active strategy on enhancing sensitivity for DNA sensing and efficient discrimination of single base mutation.

We have demonstrated the proof-of-principle of electric field assisted surface plasmon-coupled directional emission (E-SPCDE). The combination of SPCDE and electric field control produced a significant synergistic effect to amplify the right signal and suppress the wrong signal intelligently in an active strategy. A novel hairpin structured DNA biosensor based on the quenching and enhancing of fluorescence in SPCDE has been designed. With modulation of the fluorescence coupling efficiency, a high discrimination ratio up to more than 20-fold has been achieved by enhancing the signal of match and suppressing that of mismatch. E-SPCDE has shown a successful application in DNA sensing, eliminating false positives and false negatives in the detection. E-SPCDE should provide an opportunity to create a new generation of miniaturized high-performance sensing platforms especially in chip-based microarrays and to make the manipulation of the nanometer-scale processes more accessible and detectable.

Surface plasmon-coupled directional emission based on a conformational-switching signaling aptamer.

We have observed highly polarized and directional surface plasmon-coupled emission of a signaling aptamer due to the binding of a target thrombin with the aptamer, which induces conformational switching.

Adsorption of a protein-porphyrin complex at a liquid-liquid interface studied by total internal reflection synchronous fluorescence spectroscopy.

Interfacial analysis has attracted more and more attention owing to its fundamental and biological importance. Total internal reflection fluorescence (TIRF) spectroscopy is a useful method to study interfacial properties. The synchronous scanning fluorescence technique provides a selective tool to analyze a specific component in a complex system. The interaction and adsorption of bovine serum albumin (BSA) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) at toluene-water interface were studied successfully by the coupling technique of total internal reflection synchronous fluorescence (TIRSF). New methods are provided for the determination of the critical micelle concentration (cmc), apparent adsorption equilibrium constant (K(ad)) and maximum amount of adsorption (f(max)) at the liquid-liquid interface. The results indicated that BSA could adsorb onto the toluene-water interface as a complex of BSA-TPPS in a ratio of 1:1 ratio based on Langmuir adsorption isothermal model. The cmc, apparent K(ad) and f(max) for BSA at pH 3.1 were determined to be 1.0 x 10(-4) mol L(-1), 1.15 x 10(5) L mol(-1) and 1.14 x 10(-9) mol cm(-2), respectively.

Fluorescence spectral properties of rhodamine 6G at the silica/water interface.

In this work, total internal reflection synchronous fluorescence spectroscopy (TIRSF) is applied successfully to investigate rhodamine 6G (R6G) at the silica/water interface. In comparison with the bulk spectra, 5 nm red shift is observed in the interface spectra, which is mainly due to the limitation of freedom of rotational movement of R6G molecules at the interface. The increase of R6G concentration induces the self-quenching of adsorbate at the interface. The dependence of interfacial fluorescence on the acidity and ionic strength was studied. Both the acidity and ionic strength affect the adsorptive behaviors of R6G at the silica/water interface.