Gabriela F. Giordano

Optical paper-based sensor for ascorbic acid quantification using silver nanoparticles

In this paper, we demonstrate for the first time the use of silver nanoparticles (AgNPs) for colorimetric ascorbic acid (AA) quantification in a paper-based sensor. This device is constituted by spot tests modified with AgNPs and silver ions bordered by a hydrophobic barrier which provides quantitative and fast analysis of AA. In addition, this device is employed as point-of-care monitoring using a unique drop of the sample. AgNPs paper-based sensor changed from light yellow to gray color after the addition of AA due to nanoparticle growth and clusters formation. The color intensities were altered as a function of AA concentration which were measured by either a scanner or a homemade portable transmittance colorimeter. Under the selected measurement conditions, results presented limit of detection which was comparable to analytical laboratory-based methodologies. In addition, the sensitivity of our sensor was comparable to the standard titration method when real samples were investigated.

An integrated platform for gas-diffusion separation and electrochemical determination of ethanol on fermentation broths

An integrated platform was developed for point-of-use determination of ethanol in sugar cane fermentation broths. Such analysis is important because ethanol reduces its fuel production efficiency by altering the alcoholic fermentation step when in excess. The custom-designed platform integrates gas diffusion separation with voltammetric detection in a single analysis module. The detector relied on a Ni(OH)2-modified electrode. It was stabilized by uniformly depositing cobalt and cadmium hydroxides as shown by XPS measurements. Such tests were in accordance with the hypothesis related to stabilization of the Ni(OH)2 structure by insertion of Co(2+) and Cd(2+) ions in this structure. The separation step, in turn, was based on a hydrophobic PTFE membrane, which separates the sample from receptor solution (electrolyte) where the electrodes were placed. Parameters of limit of detection and analytical sensitivity were estimated to be 0.2% v/v and 2.90 μA % (v/v)(-1), respectively. Samples of fermentation broth were analyzed by both standard addition method and direct interpolation in saline medium based-analytical curve. In this case, the saline solution exhibited ionic strength similar to those of the samples intended to surpass the tonometry colligative effect of the samples over analyte concentration data by attributing the reduction in quantity of diffused ethanol vapor majorly to the electrolyte. The approach of analytical curve provided rapid, simple and accurate analysis, thus contributing for deployment of point-of-use technologies. All of the results were accurate with respect to those obtained by FTIR method at 95% confidence level.

Portable platform for rapid and indirect photometric determination of water in ethanol fuel samples

We have developed a simple, fast, portable, inexpensive, and indirect method for the determination of water in ethanol fuels. The addition of an excess amount of water is the most simple and common method of adulterating these fuels. Such procedure can adversely affect the performance of the vehicle. Our system uses a laboratory-made photometry device to monitor the formation of complexes between ethanol and cerium(IV). These reactions produce deep orange–red solutions. The limit of detection and the analytical sensitivity were estimated to be 0.22% v/v (water in ethanol) and 0.11 (% v/v)−1, respectively. The developed platform was satisfactorily robust with respect to the changes in temperature and stability of the reagents during storage. The measurements were accurate at the 95% confidence level compared with data obtained by Karl Fischer titration.

Microemulsification-based method: analysis of ethanol in fermentation broth of sugar cane

This article addresses important results for the consolidation of the microemulsification-based method (MEC), an approach recently proposed by these authors, which represents a powerful output for the deployment of point-of-use technologies. In MEC, the detection is conducted in a solution with the naked eyes. It relies on the effect of the analyte on the formation of microemulsions (MEs). The minimum volume fraction of amphiphile needed to obtain ME (ΦME) is the analytical response whose measurement is based on binary chemical information: the cloudy-to-transparent transition that occurs with microemulsification. Accordingly, this signal can be precisely detected with the naked eye, thus enabling precise determinations. The experiments that were accomplished are as follows: robustness investigation and the direct determination of ethanol in fermentation broths of sugar cane. Dispersions were composed of water, oleic acid, and ethanol as hydrophilic (W), hydrophobic (O), and amphiphilic (AP) phases, respectively. Standards of analyte were added to the W phase before the addition of AP in the W–O mixture to attain the analytical curves. For application, the samples were directly used as the W phase. Our approach was somewhat robust with regard to deviations in volumetric preparation of the dispersions and changes in temperature and conductivity. Lastly, the reliability of the MEC was evaluated in the determination of ethanol in fermentation broths of sugar cane. The results were astoundingly accurate after direct analyses with the naked-eye detection. Usually, for these samples the dilution and separation steps require tools such as chromatography and electrophoresis. Limit of linearity, analytical sensitivity, and limit of detection were 70.00% v/v ethanol to water, −0.39, and 1.34% v/v, respectively. MEC stands out in relation to the other methods reported in literature for the determination of ethanol in alcoholic beverages and fermentation broths when considering parameters of wide linearity and low-cost. Indeed, our method is unique in ensuring precise determinations without instrumental detection, requiring only the naked eye. It represents a remarkable aspect for point-of-use measurements. In contrast, MEC is not applicable for trace chemical analyses because of its poor limit of detection.

Microemulsification-Based Method: Coupling with Separation Technique

The outcomes described herein outline the potentiality of the microemulsification-based method (MEC) for development of rapid testing (point-of-use) technologies. MEC was recently proposed by these authors for analytical determinations wherein the detection is conducted in solution with naked eyes. It relies on effect of analyte over the colloid thermodynamics by changing the minimum volume fraction of amphiphile needed to generate microemulsions (MEs) (ΦME), which represents the analytical response of the method. We report in this paper the successfully coupling of MEC-based detection with gas diffusion separation. Such result extends the field of application of MEC in analytical sciences by improving its selectivity. One custom-designed module was constructed on PTFE for the separation measurements. It was utilized in combination with MEC for determining water in ethanol fuels using water/ n-propanol/oleic acid MEs and water-rich compositions. In this situation, accurate direct determinations by MEC are not possible. In addition, further studies on analytical performance and robustness of MEC by using n-propanol amphiphile are described. The method was robust as regards to deviations in dispersion preparing and changes in temperature. Concerning the analytical performance, the analytical curves presented wide linear range with limits of linearity of up to 70.00% v/v ethanol to water (ΦE). The limits of detection (S/N=3) were of 1.03%, 7.21%, and 0.68% v/v ΦE for compositions with water- (region A) and oil-rich (region C) domains as well as equal volumes of water and oil phases (region B), respectively. With respect to the regions A and B, the analytical performance stressed herein exhibited best linearity and comparable sensitivities when compared to these levels reached with ethanol amphiphile (our first publication on MEC) rather than n-propanol.

Gravity-assisted distillation on a chip: Fabrication, characterization, and applications

Distillation is widely used in industrial processes and laboratories for sample pre-treatment. The conventional apparatus of flash distillation is composed of heating source, distilling flask, condenser, and receiving flask. As disadvantages, this method shows manual and laborious analyses with high consumption of chemicals. In this paper, all these limitations were addressed by developing a fully integrated microscale distiller in agreement with the apparatus of conventional flash distillation. The main challenge facing the distillation miniaturization is the phase separation since surface forces take over from the gravity in microscale channels. Otherwise, our chip had ability to perform gravity-assisted distillations because of the somewhat large dimensions of the distillation chamber (roughly 900 μL) that was obtained by 3D-printing. The functional distillation units were integrated into a single device composed of polydimethylsiloxane (PDMS). Its fabrication was cost-effective and simple by avoiding the use of cleanroom and bonding step. In addition to user-friendly analysis and low consumption of chemicals, the method requires cost-effective instrumentation, namely, voltage supply and analytical balance. Furthermore, the so called distillation-on-a-chip (DOC) eliminates the use of membranes and electrodes (usually employed in microfluidic desalinations reported in the literature), thus avoiding drawbacks such as liquid leakage, membrane fouling, and electrode passivation. The DOC promoted desalinations at harsh salinity (NaCl 600.0 mmol L-1) with high throughput and salt removal efficiency (roughly 99%). Besides, the method was used for determination of ethanol in alcoholic beverages to show the potential of the approach toward quantitative purposes.

Intervening factors in the performance of a naked-eye microemulsification-based method and improvements in analytical frequency

An investigation into the use of different amphiphiles and improvements in the analytical frequency of the microemulsification-based method (MEC) are described. The results are important for improving the understanding of the method (recently proposed by our group) and the development of attractive screening analysis platforms. MEC ensures precise determination with the naked eye, providing a powerful alternative to other point-of-use experiments. Herein, the influence of different surfactant-based amphiphiles (AP) on MEC analytical performance was exhaustively evaluated for the first time, including ionic (sodium dodecylsulphate, SDS, and cetyl trimethylammonium bromide, CTAB) and neutral (triton X-100, TX-100, and tergitol NP-9, TNP-9) surfactants. The analytical performance was investigated for each of the APs in three dispersion compositions according to precision, linearity, robustness, and accuracy, which were obtained for the determination of ethanol (% v/v) in water and commercial alcoholic beverages. The data obtained for TNP-9 showed poor robustness as a function of deviations in the oil phase volume and ionic strength. Additionally, CTAB exhibited unsatisfactory robustness as a function of temperature changes. In summary, TX-100 and SDS in regions A and B, and CTAB in region A, gave the best analytical performance in the determination of ethanol in alcoholic beverages. Furthermore, a new experimental mode was developed to increase the capacity of MEC for rapid analysis of various samples. This procedure was based on semi-quantitative analyses using a 96-deep-well plate (DWP) and a multichannel micropipette to prepare the dispersions. This assembly allowed naked-eye screening analysis of up to 12 samples with a resolution of eight concentration ranges in a single run without subjective uncertainties, even after storing the DWP at 4 °C for at least five weeks. This approach has advantages including rapidity, simplicity, portability, and low cost, making it a promising alternative for continuous quality control in many industrial processes.