Janus Hydrogel Microbeads for Glucose Sensing with pH Calibration

We present fluorescent Janus hydrogel microbeads for continuous glucose sensing with pH calibration. The Janus hydrogel microbeads, that consist of fluorescent glucose and pH sensors, were fabricated with a UV-assisted centrifugal microfluidic device. The microbead can calibrate the pH values of its surroundings and enables accurate measurements of glucose within various pH conditions. As a proof of concept, we succeeded in obtaining the accurate value of glucose concentration in a body-fluid-like sample solution. We believe that our fluorescent microbeads, with pH calibration capability, could be applied to fully implantable sensors for continuous glucose monitoring.

On-the-go tropical soil sensing for pH determination using ion-selective electrodes

The objective of this work was to assess the performance of an antimony ion-selective electrode (ISE) sensor system, using manual and automatic operating modes, for measuring the potential of hydrogen (pH), in real time, in Oxisols with different characteristics. Samples were manually collected and sent to a laboratory for determination of pH in water and calcium chloride, whose values were used as references. Another set of samples was also automatically collected using a commercial equipment, and readings were performed in manual mode. The performance parameters of the sensor system were calculated and evaluated. Part of the soil samples was used to assess the degree of influence of moisture in determining pH. Calibration lines were constructed. The statistical analysis revealed better results for the manual mode. Both modes of operation had errors superior to those accepted as a limit in laboratory techniques, however, with the possibility of high data density and with positive and promising results. Soil moisture interfered with the result of the readings. The sensor system yields a sampling density of 45 data per hectare, which represents a great contribution to the intensification of data for a better spatial evaluation of soil information.

A 5 pH Point Titration Method for Determining the Carbonate and SCFA Weak Acid/Bases in Anaerobic Systems

A 5 pH point acid titration method is proposed to measure the short chain fatty acids, total carbonate species concentration and H2CO3*alkalinity in anaerobic systems. To test the method, aqueous solutions containing NaHCO3 (1990; 2488 mg/ℓ as CaCO3) and the short chain fatty acid (SCFA) acetic acid with concentrations ranging from 100 to 1000 mg/ℓ were titrated using the method; the H2CO3*alkalinity and SCFA estimates ranged around the expected values with an average standard deviation of 5 and 8 percent respectively. Estimates of the SCFA by the method and by Montgomery et al 's wet chemical method on the effluents of UASB reactors treating brewery and wine distillery waste correlated closely (r = 0.98). Other tests demonstrated as predicted that the presence of ammonium has a negligible effect on the derived results. However, phosphates can have a significant effect on the H2CO3*alkalinity but not on the SCFA estimates. The phosphate effect is eliminated in the derived estimates if its concentration is known. The method also identifies errors in pH due to the residual liquid junction effect or poor calibration and corrects the estimates accordingly; deliberately imposed pH calibration errors were identified and their error effects on the H2CO3*alkalinity and SCFA estimates largely corrected.

Diatom-inferred pH calibration of lakes near Wawa, Ontario

In the absence of long-term pH records for lakes, sedimentary diatoms have often been used to detect the extent of recent lake acidification. Although various methods have been used to relate surface-sediment diatom remains to contemporary lake-water pH, their usefulness and selection criteria have not been clearly defined for Canadian lakes. Surface-sediment diatoms of 28 lakes (pH 4.0–8.13) located northeast of Lake Superior were identified and enumerated. Lake-water pH estimates were made using multiple regression analyses of selected diatom taxa and Hustedt's pH indicator groups, as well as by index α and index B. Multiple regression, using the abundance of pH indicator assemblages, appears to be the most suitable method for the studied lake region. Discrepancies associated with other methods are discussed in details.