Label free detection of multiple trace antibiotics with SERS substrates and independent components analysis.

Surface enhanced Raman spectroscopy (SERS) has been widely studied and recognized as a powerful label-free technique for trace chemical analysis. However, its drawback in simultaneously identifying several molecular species has greatly limited its real-world applications. In this work, we reported a combination between SERS and independent component analysis (ICA) to detect several trace antibiotics which are commonly used in aquacultures, including malachite green, furazolidone, furaltadone hydrochloride, nitrofurantoin, and nitrofurazone. The analysis results indicate that the ICA method is highly effective in decomposing the measured SERS spectra. The target antibiotics could be precisely identified when the number of components and the sign of each independent component loading were properly optimized. With SERS substrates, the optimized ICA can identify trace molecules in a mixture at a concentration of 10-6 M achieving the correlation values to the reference molecular spectra of 71-98%. Furthermore, measurement results obtained from a real-world sample demonstration could also be recognized as an important basis to suggest this method is promising for monitoring antibiotics in a real aquatic environment.

Hybrid optical-electrochemical electronic nose system based on Zn-porphyrin and multi-walled carbon nanotube composite.

In this work, we have enhanced the capability of an e-nose system based on combined optical and electrochemical transduction within a single gas sensor array. The optical part of this e-nose is based on detection of the absorption changes of light emitted from eight light emitting diodes (LEDs) as measured by a CMOS photo-detector. The electrochemical part works by measuring the change in electrical resistivity of the sensing materials upon contact with the sample vapor. Zinc-5,10,15,20-tetra-phenyl-21H,23H-porphyrin (ZnTPP) and multi-walled carbon nanotube (MWCNT) composite was used as the sensing materials based on its good optoelectronic properties. This sensing layer was characterized by UV-Vis spectroscopy and atomic force microscope and tested with various VOC vapors. Density functional theory (DFT) calculations were performed to investigate the electronic properties and interaction energies between ZnTPP and analyte molecules. It can be clearly seen that this hybrid optical-electrochemical electronic nose system can classify the vapor of different volatile organic compounds.

Enhancement of DNA hybridization under acoustic streaming with three-piezoelectric-transducer system.

Recently, we have demonstrated that DNA hybridization using acoustic streaming induced by two piezoelectric transducers provides higher DNA hybridization efficiency than the conventional method. In this work, we refine acoustic streaming system for DNA hybridization by inserting an additional piezoelectric transducer and redesigning the locations of the transducers. The Comsol® Multiphysics was used to design and simulate the velocity field generated by the piezoelectric agitation. The simulated velocity vector followed a spiral vortex flow field with an average direction outward from the center of the transducers. These vortices caused the lower signal intensity in the middle of the microarray for the two-piezoelectric disk design. On the contrary, the problem almost disappeared in the three-piezoelectric-disk system. The optimum condition for controlling the piezoelectric was obtained from the dye experiments with different activation settings for the transducers. The best setting was to activate the side disks and middle disk alternatively with 1 second activating time and 3 second non-activating time for both sets of transducers. DNA hybridization using microarrays for the malaria parasite Plasmodium falciparum from the optimized process yielded a three-fold enhancement of the signal compared to the conventional method. Moreover, a greater number of spots passed quality control in the optimized device, which could greatly improve biological interpretation of DNA hybridization data.

DNA hybridization enhancement using piezoelectric microagitation through a liquid coupling medium.

In conventional DNA microarray hybridization, delivery of target cDNAs to surface-bounded probes depends solely on diffusion, which is notoriously slow, and thus typically requires 6-20 h to complete. In this study, piezoelectric microagitation through a liquid coupling medium is employed to enhance DNA hybridization efficiency and the results are compared with the standard static hybridization method. DNA hybridization was performed in a sealed aluminium chamber containing DNA microarray glass chip, coupling medium and piezoelectric transducers. 3×SSC (Saline Sodium Citrate) was used as a coupling medium to prevent overheating of the piezoelectric transducers and to effectively transmit ultrasonic wave to the glass chip. Flow visualization using fluidic dye and velocimetry (PTV) technique was applied to observe fluid transport in the hybridization chamber. It was revealed that the dye solution was homogeneously distributed within 10 min under dynamic agitation while it took over 1 h to reach the same level of homogeneity in static condition. Plasmodium falciparum DNA microarrays and total RNA extracted from parasite cells were used as a model for DNA microarray experiments. It was found that the required hybridization time may be substantially reduced from 16 h to 4 h by the use of dynamic hybridization scheme. With the same hybridization time of 16 h, dynamic hybridization resulted in higher fluorescent signals of ∼33% and ∼24% compared to static hybridization in Cy3 and Cy5 channels, respectively. Additionally, good/effective spots, some of which were not formed by static method, were enhanced and distributed more uniformly over the microarray. Therefore, the developed dynamic hybridization with integrated piezoelectric microagitation platform is highly promising for DNA analysis in molecular biology and medical applications.