Sequentially addressable dielectrophoretic array for high-throughput sorting of large-volume biological compartments.

Droplet microfluidics has become a powerful tool in precision medicine, green biotechnology, and cell therapy for single-cell analysis and selection by virtue of its ability to effectively confine cells. However, there remains a fundamental trade-off between droplet volume and sorting throughput, limiting the advantages of droplet microfluidics to small droplets (<10 pl) that are incompatible with long-term maintenance and growth of most cells. We present a sequentially addressable dielectrophoretic array (SADA) sorter to overcome this problem. The SADA sorter uses an on-chip array of electrodes activated and deactivated in a sequence synchronized to the speed and position of a passing target droplet to deliver an accumulated dielectrophoretic force and gently pull it in the direction of sorting in a high-speed flow. We use it to demonstrate large-droplet sorting with ~20-fold higher throughputs than conventional techniques and apply it to long-term single-cell analysis of Saccharomyces cerevisiae based on their growth rate.

[The effect of ammonium fluoride solution at various concentrations on enamel].

The fluoride concentrations of ammonium fluoride solution (NH4F,pH 4.4), which has the same effect on enamel powder as conventional APF solution, were studied. Human enamel powder (200 mesh passed) was treated with solutions of NH4F (1,000 ppmF-, 3,000 ppmF-, 5,000 ppmF-, 7,000 ppmF-, 9,000 ppmF-, pH 4.4) and APF (9,000 ppmF-, pH 3.4) for 5 min. at 37 degrees C. Some of the specimen was washed with 1MKOH solution for 48 hours. Fluoride uptake by enamel powder was analyzed by means of chemical analysis and reaction products identified using X-ray diffractometry. The fluoride uptake of 5,000 ppmF- of NH4F-treated enamel was the same as that of APF-treated enamel. X-ray diffractometry showed that CaF2 was formed in the experimental groups. CaF2 with high crystallinity was formed in the NH4F-treated enamel, and the peak height of X-ray diffraction pattern of CaF2 in 3,000 ppmF- of NH4F-treated enamel was the same as that of APF-treated enamel. In conclusion, the ammonium fluoride solution of 3,000-5,000 ppmF- had a similar effect on enamel powder as conventional APF solution.

[Cohort study on cariostatic effect of 100ppmF- fluoride mouthrinsing].

The cariostatic effect of fluoride mouthrinsing with dilute fluoride solution in the school dental health programs was examined. The subjects were 138 children (75 of boys and 63 of girls) who carried out fluoride mouthrinsing with solution of 100 ppmF- for 6 years and 105 children (65 of boys and 40 of girls) who had no fluoride mouthrinsing were analysed by cohort study from 1983 to 1989. The cariostatic effect was evaluated by DMFT index and DMF rate for each tooth type in each erupted school grade. The increment of DMFT index was less than that of the control group. There was a clear cariostatic effect with the advance in the school grade. DMF rate for each tooth type of 1 in 2nd grade and 2 in 3rd grade students showed a statistically significant difference. Both that of upper and lower first molars in 1st and 2nd grade also showed the same result as that of upper incisors. In conclusion, a high cariostatic effect was obtained by introducing the use of fluoride mouthrinsing with a solution of 100ppmF- to the school dental health program, and the observation of DMF rate for each tooth type classified with each erupted school grade was a useful method to evaluate the cariostatic effect of fluoride mouthrinsing.

Enzyme-linked immunosorbent assay for 17 alpha-hydroxyprogesterone in dried blood spotted on filter paper.

In this rapid, cost-effective, enzyme-linked immunosorbent assay for 17 alpha-hydroxyprogesterone (17-OHP) eluted from dried blood spotted on filter paper, second antibody is coated onto the microwell plate and horseradish peroxidase (EC 1.11.1.7) is the label enzyme. Antiserum to 17-OHP was prepared by using 4-(2-carboxymethylthio)-17-OHP-bovine serum albumin conjugate as immunogen. Enzyme conjugate was prepared from 4-(2-carboxymethylthio)-17-OHP and peroxidase. The blood spots are assayed in the microwells without extraction or centrifugation steps. The detection limit of the assay is 1 microgram/L, equivalent to 3.5 pg (10.6 fmol) per disc. Intra- and interassay CVs at two steroid concentrations (7.38 and 22.79 micrograms/L) ranged from 3.74 to 11.90% (n = 5), and 9.49 and 9.83% (n = 5), respectively. Results correlated well (r = 0.91) with those of a fluorescence enzyme immunoassay. The sensitivity, specificity, and precision of this method make it potentially useful in the mass screening of neonates for congenital adrenal hyperplasia.

Screening for bacteriuria in healthy Japanese school children.

Bacteriuria was screened among 28,202 healthy school children, 14,575 boys and 13,627 girls by dipstick and dipslide methods and also by pour plate culture method. Prevalence of bacteriuria was 0.06% in boys and 0.54% in girls after third screening. A high rate of false negative results with dipstick test and a high rate of false positive results with dipslide culture method using Microstix-3 were observed. About 60% of screened children continued to have bacteriuria persistently for 9 months after third screening followed by monthly urine culture. Anomalies of urinary tract were detected in 9 of 26 children with persistent bacteriuria.