Zoraida P. Aguilar

Fluorescent Ru(phen)32+-Doped Silica Nanoparticles-Based ICTS Sensor for Quantitative Detection of Enrofloxacin Residues in Chicken Meat

A Ru(phen)3(2+)-doped silica fluorescent nanoparticle (FN)-based immunochromatographic test strip (ICTS) sensor was developed for rapid, high sensitivity, easy to use, and low cost quantitative detection of enrofloxacin (ENR) residues in chicken meat. The fluorescence signal intensity of the FNs at the test line (FI(T)) and control line (FI(C)) was determined with a prototype of a portable fluorescent strip reader. Unique properties of Ru(phen)3(2+) doped silica nanoparticles (e.g., large Stokes shift, high emission quantum yield, and long fluorescence lifetime) were combined with the advantages of ICTS and an easy to make portable fluorescent strip reader. The signal was based on FI(T)/FI(C) ratio to effectively eliminate strip to strip variation and matrix effects. Various parameters that influenced the strip were investigated and optimized. Quantitative ENR detection with the FNs ICTS sensor using 80 μL sample took only 20 min, which is faster than the commercial ELISA kit (that took 90 min). The linear range of detection in chicken extract was established at 0.025-3.500 ng/mL with a half maximal inhibitory concentration at 0.22 ± 0.02 ng/mL. Using the optimized parameters, the limit of detection (LOD) for ENR using the FNs ICTS sensor was recorded at 0.02 ng/mL in chicken extract. This corresponds to 0.12 μg/kg chicken meat which is two (2) orders of magnitude better that the maximum residue limits (MRLs) imposed in Japan (10 μg/kg) and three (3) orders of magnitude better than those imposed in China. The intra- and inter-assay coefficient of variations (CVs) were 6.04% and 12.96% at 0.5 ng/mL, 6.92% and 12.61% at 1.0 ng/mL, and 6.66% and 11.88% at 2.0 ng/mL in chicken extract, respectively. The recoveries using the new FNs ICTS sensor from fifty (50) ENR-spiked chicken samples showed a highly significant correlation (R(2) = 0.9693) with the commercial enzyme-linked immunosorbent assay (ELISA) kit. The new FNs ICTS sensor is a simple, rapid, sensitive, accurate, and inexpensive quantitative detection of ENR residues in chicken meat and extracts.

Characterization and Pumping Redox Magnetohydrodynamics in a Microfluidic Channel

By adding redox species, both aqueous and nonaqueous solutions can be pumped along the length of a microfluidic channel when low voltages (to produce current) are applied across the channels breadth in the presence of a magnetic field applied across its height. Control of flow rate is possible by varying the magnitudes of the voltage and magnetic field and by changing the redox concentration. Direction is determined by the voltage polarity and magnetic field orientation. We have demonstrated a dc redox magnetohydrodynamic (MHD) pump in microchannels (270 μm wide × 640 μm deep X 2 cm long) that were constructed from low-temperature cofired ceramics with screen-printed gold electrodes on opposing sidewalls. Redox MHD involves the generation of current between the electrodes in a solution through the oxidation/reduction of redox species in the presence of a magnetic field. When the current and magnetic fields are perpendicular, a Lorentz force results, causing fluid flow along the length of the channel. The pumping performance was investigated as a function of type and concentration of redox species, magnetic flux density, applied voltage, and time scale. Studies show bidirectional capability by changing the direction of the current. Flow velocities of up to 5.0 mm/s were observed in a solution of 0.5 M nitrobenzene (NB) and 0.5 M tetrabutylammonium hexafluorophosphate (TBAPF 6 ) in acetonitrile using a 0.41 T NdFeB permanent magnet, at an applied voltage of -1.3 V vs Ag/AgCl (saturated KCl) (approximately a potential difference of 1.2-1.7 V between wall electrodes in the microchannel) and the corresponding current enhancements (caused by the increased convection) were as large as 145%. Flow rates for 0.1 M NB and 0.25 M NB in 0.1 M TBAPF 6 in acetonitrile were measured at three different applied voltages near the redox potential of NB. Comparisons were also made to theory. A mixture of oxidized and reduced forms of the same redox couple, instead of a single species like NB, can avoid electrode dissolution at the oxidizing electrode (or bubble generation at either electrode). One example of this approach involves a solution of 0.125 M Fe 2+ and 0.125 M Fe 3+ in 3.0 M KCl and another involves a solution of 0.125 M Fe(CN) 3- 6 and 0.125 M Fe(CN) 4- 6 in 2.0 M KCl, where potential differences between wall electrodes in the microchannel can be less than 0.4 V. Findings from these studies should be useful in development of sealed microanalytical devices using redox MHD pumps with possible lab-on-a-chip applications.

Electrochemical Immunoassay Detection of Bacillus Anthracis Protective Antigen

A self-contained microelectrochemical immunoassay detection of Bacillus anthracis protective antigen (PA) has been developed. A microcavity array (VEG4x1TM) of 50-μm diameter cavities with self-contained microelectrodes were used for the detection of as low as 2.5 pg of B. anthracis Protective Antigen in a less than 12 min total assay time from capture to signal generation. The microelectrochemical sandwich enzyme-linked immunoassay involved covalent immobilization of the capture antibody on the free end of mercaptoundecanol self-assembled monolayers at the bottom Aumicrodisk electrode that also serves as the bottom of the microcavities. Signal generation involved alkaline phosphatase hydrolysis of the enzyme substrate p-aminophenyl phosphate to paminophenol that is detected with the wall middle layer gold as the detecting electrode and the top layer gold as the pseudoreference/auxiliary electrodes. The microelectrodes in the cavity exhibited background signals lower than signal for the lowest concentration detected that was 2.5 pg.