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3.
Lab Chip ; 20(8): 1441-1448, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32211667

RESUMO

A wide range of microfluidic paper-based analytical devices (µPADs) have been developed in the last decade. Despite this, the quality of colorimetric analysis has not substantially improved as the data is vulnerable to heterogeneous color distribution (e.g., coffee ring effects), non-uniform shapes of colored detection area, and noise from the underlying paper structure. These limitations are here addressed by a colorimetric method to quantify freely discharged dye on paper substrate, without the need for a defined channel or hydrophobic barrier. For accurate quantification, colorimetric absorbance values are calculated for each pixel based on the recorded RGB values and noise from the paper structure eliminated, to extract accurate absorbance information at the pixel level. Total analyte quantity is then calculated through the conversion of absorbance values into quantity values for each pixel followed by integration across the entire image. The resulting quantity is shown to be independent of the shape of the applied colored dye spot, with a cross, circle or rod shape all giving the same quantity information. The approach is applied to a capillary-based potassium-selective sensor, where the sample solution is loaded with the dye thioflavin T (ThT) obtained by quantitative exchange with K+ in a sensing capillary, which is discharged onto a bare paper substrate without any channels. The resulting dye quantity is successfully obtained by flatbed scanner and smartphone. The successful automated computation of colorimetric data on µPADs will help realize simpler paper-based assay and reaction systems that should be more applicable to addressing real world analytical problems.

4.
ACS Sens ; 5(3): 650-654, 2020 03 27.
Artigo em Inglês | MEDLINE | ID: mdl-32106675

RESUMO

Potentiometric pH probes remain the gold standard for the detection of pH but are not sufficiently sensitive to reliably detect ocean acidification at adequate frequency. Here, potentiometric probes are made dramatically more sensitive by placing a capacitive electronic component in series to the pH probe while imposing a constant potential over the measurement circuit. Each sample change now triggers a capacitive current transient that is easily identified between the two equilibrium states, and is integrated to reveal the accumulated charge. This affords dramatically higher precision than with traditional potentiometric probes. pH changes down to 0.001 pH units are easily distinguished in buffer and seawater samples, at a precision (standard deviation) of 28 µpH and 67 µpH, respectively, orders of magnitude better than what is possible with potentiometric pH probes.

5.
ACS Sens ; 5(2): 313-318, 2020 02 28.
Artigo em Inglês | MEDLINE | ID: mdl-32050757

RESUMO

Potentiometric probes used in direct potentiometry are attractive sensing tools. They give information on ion activities, which is often uniquely useful. If, instead, concentrations are desired as sensor output, the ionic strength of the sample must be precisely known, which is often not possible. Here, for the first time, direct potentiometry can be made to report concentrations, rather than activities. It is demonstrated for the detection of monovalent anionic species by using a self-referencing Ag/AgI pulstrode as the reference element instead of a traditional reference electrode. This reference pulstrode releases a discrete quantity of iodide ions from the electrode and the resulting reference potential varies with the activity coefficient of iodide. The effects of activity coefficient on the indicator and reference electrode are therefore compensated and the observed cell potential may now be described in a Nernstian manner against anion concentration, rather than activity. Theoretical simulations and experimental results support the validity of this approach. For most monovalent anions of practical relevance, the potential difference between this approach and from a traditional activity coefficient calculation is less than 0.5 mV. The concept is validated with an all-solid-state nitrate sensor as well as a commercial fluoride-selective electrode, giving Nernstian responses in different ionic strength backgrounds against concentration without the need for correcting activity coefficients or liquid junction potentials.

7.
Anal Chem ; 92(4): 2926-2930, 2020 02 18.
Artigo em Inglês | MEDLINE | ID: mdl-31994386

RESUMO

The sensitivity of potentiometric sensors functioning in equilibrium mode is limited by the value predicted according to the Nernst equation and inversely proportional to the charge in the analyte ion. Therefore, an increased ion charge results in a dramatic decrease in the sensor sensitivity. We propose an approach to allow one to increase the sensitivity of the potentiometric measurements by using a combined electrochemical cell composed of several identical ion-selective electrodes immersed into separate sample solutions of equal composition. The combination of n electrodes, demonstrating individually a Nernstian slope in one electrochemical cell allows to amplify the signal and associated response slope by n times. The proposed approach is shown to provide a double and triple Nernstian slope for potassium-, calcium-, nitrate-, and carbonate-selective electrodes by combining two or three identical electrodes, correspondingly. Each ion-selective electrode functions in an equilibrium mode, hence, ensuring response stability and reproducibility.

8.
Int J Dent Hyg ; 18(1): 27-43, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31054209

RESUMO

OBJECTIVES: To investigate whether chlorhexidine mouthwash (CHX-MW), with an anti-discoloration system(ADS), is effective in preventing extrinsic tooth surface discoloration. Additionally, this paper seeks to evaluate whether CHX combined with an ADS maintains its efficacy with respect to reducing plaque and gingivitis scores. MATERIAL AND METHODS: MEDLINE-PubMed and Cochrane-Central were searched up to October 2018 to identify eligible studies. Papers evaluating the effect of CHX-MW+ADS compared to CHX without an ADS were included. A descriptive analysis and when feasible a meta-analysis was performed. RESULTS: Screening resulted in 13 eligible publications, presenting 16 comparisons. Six of these evaluated the MW in a non-brushing model and ten as an adjunct to toothbrushing. A descriptive analysis demonstrated that the majority showed no differences in bleeding, gingivitis and plaque scores. This was confirmed by the meta-analysis. In non-brushing experiments, the difference-of-means (DiffM) for plaque scores was 0.10 (P = 0.45, 95%CI: [-0.15; 0.34]) and for the gingival index 0.04 (P = 0.15,95%CI: [-0.02; 0.11]). The DiffM in brushing studies for plaque scores was 0.01 (P = 0.29, 95%CI: [-0.01; 0.02]) and for the gingival index 0.00 (P = 0.87,95%CI: [-0.05; 0.06]). With respect to staining scores, the meta-analysis revealed that in non-brushing studies, the standardized mean difference was 3.19 (P = 0.0005,95%CI: [-3.98; -1.41]) while in brushing studies, the DiffM was 0.12 (P = 0.95,95%CI: [-3.32; 3.55]). CONCLUSION: There is moderate quality evidence from non-brushing studies that the addition of an ADS to CHX-MW reduces tooth surface discoloration and does not appear to affect its properties with respect to gingival inflammation and plaque scores. In brushing studies, there is also moderate quality evidence that ADS does not affect the anti-plaque and anti-gingivitis efficacy of CHX. The majority of comparisons and the meta-analysis including these indicate no significant effect of ADS on tooth staining in situations where the mouthwash is used in addition to toothbrushing.


Assuntos
Anti-Infecciosos Locais , Placa Dentária , Gengivite , Descoloração de Dente , Clorexidina , Humanos , Antissépticos Bucais
9.
Angew Chem Int Ed Engl ; 59(6): 2294-2298, 2020 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-31714666

RESUMO

The design of solid-state reference electrodes without a liquid junction is important to allow miniature and cost-effective electrochemical sensors. To address this, a pulse control is proposed using an Ag/AgI element as reliable solid-state reference electrode. It involves the local release of iodide by a cathodic current that is immediately followed by an electromotive force (EMF) measurement that serves as the reference potential. The recapture of iodide ions is achieved by potentiostatic control. This results in intermittent potential values that are reproducible to less than one millivolt (SD=0.27 mV, n=50). The ionic strength is shown to influence the activity coefficient of released iodide in accordance with the extended Debye-Hückel equation, resulting in a predictable change of the potential reading. The principle is applied to potentiometric potassium detection with a valinomycin-based ion-selective electrode (ISE), demonstrating a completely solid-state sensor configuration.

10.
Chimia (Aarau) ; 73(11): 944, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31753077
11.
ACS Sens ; 4(12): 3093-3101, 2019 Dec 27.
Artigo em Inglês | MEDLINE | ID: mdl-31744290

RESUMO

Colorimetric measurements by image analysis, giving RGB or HSV data, have become commonplace with optical indicator-based assays and as a readout for paper-based analytical devices (PADs). Yet, most works on PADs tend to ignore the quantitative relationship between color data and concentration, which may hamper their establishment as analytical devices and make it difficult to properly understand chemical or biological reactions on the paper substrate. This Perspective Article discusses how image color data are computed into colorimetric absorbance values that correlate linearly to dye concentration and compare well to traditional spectrophotometry. Thioflavin T (ThT), Neutral Red (NR), and Orange IV are used here as model systems. Absorbance measurements in solution correlate well to image data (and Beer's law) from the color channel of relevance if the gamma correction normally used to render the picture more natural to the human eye is removed. This approach also allows one to correct for color cast and variable background color, which may otherwise limit quantitation in field measurements. Reflectance measurements on paper color spots are equally found to correlate quantitatively between spectroscopy and imaging devices. In this way, deviations from Beer's law are identified that are explained with dye interactions on the paper substrate.

12.
Chem Commun (Camb) ; 55(83): 12539-12542, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31576840

RESUMO

A range of ionic solvatochromic dye (SD) transducers for use in ion-selective emulsified optical sensors are introduced and characterized. They share the same chromophore group, (E)-4-(4-(dimethylamino)styryl)pyridinium, but vary in their lipophilicities by grafted alkyl or ethoxy groups. The calibration curve is found to shift by a total of 2.7 orders of magnitude with the lipophilicity of the SD.

13.
J Knee Surg ; 2019 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-31634936

RESUMO

Multiple studies found hamstring tendon (HT) autograft diameter to be a risk factor for anterior cruciate ligament (ACL) reconstruction failure. This study aimed to determine which preoperative measurements are associated with HT autograft diameter in ACL reconstruction by directly comparing patient characteristics and cross-sectional area (CSA) measurement of the semitendinosus and gracilis tendon on magnetic resonance imaging (MRI). Fifty-three patients with a primary ACL reconstruction with a four-stranded HT autograft were included in this study. Preoperatively we recorded length, weight, thigh circumference, gender, age, preinjury Tegner activity score, and CSA of the semitendinosus and gracilis tendon on MRI. Total CSA on MRI, weight, height, gender, and thigh circumference were all significantly correlated with HT autograft diameter (p < 0.05). A multiple linear regression model with CSA measurement of the HTs on MRI, weight, and height showed the most explained variance of HT autograft diameter (adjusted R 2 = 44%). A regression equation was derived for an estimation of the expected intraoperative HT autograft diameter: 1.2508 + 0.0400 × total CSA (mm2) + 0.0100 × weight (kg) + 0.0296 × length (cm). The Bland and Altman analysis indicated a 95% limit of agreement of ± 1.14 mm and an error correlation of r = 0.47. Smaller CSA of the semitendinosus and gracilis tendon on MRI, shorter stature, lower weight, smaller thigh circumference, and female gender are associated with a smaller four-stranded HT autograft diameter in ACL reconstruction. Multiple linear regression analysis indicated that the combination of MRI CSA measurement, weight, and height is the strongest predictor.

14.
ACS Sens ; 4(8): 1964, 2019 08 23.
Artigo em Inglês | MEDLINE | ID: mdl-31438683
15.
Anal Chem ; 91(14): 8973-8978, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31190528

RESUMO

It has recently been reported that polystyrene microbeads may be modified to realize plasticizer-free ion-selective optical sensors (optodes) on the basis of solvatochromic dye transducers. We show here that the functionalized microbeads, individually isolated by flow cytometry, exhibit unexpectedly poor fluorescent properties and that the sensor response is instead attributed to the supernatant. A more thorough study reveals that such optical microemulsion sensors can be made operationally functional and chemically selective, seemingly in the absence of any solvent matrix or added surfactant. Instead, it is shown that residual THF used in the fabrication of the emulsified sensors may solubilize the sensing components and give a functional optode response. To evaluate this further, the number of sensing components was stepwise simplified to assess their need. Variation of residual THF levels has no effect on the ion optode response when plasticizer is present, in support of established results. Lipophilic solvatochromic dye transducers are also shown not to require an added surfactant as their nature already endows the emulsified sensors with a stabilizing ionic surface charge. The ionophores are shown to exhibit much larger stability constants in the surfactant-free formulations than surfactant-based ones (valionomycin, log ß > 9.2 compared to 6.1; Na+-ionophore X, 6.7 vs 4.7), which is attributed to a less polar solvent environment for the ionophore. Potassium-, sodium-, and calcium-selective sensors were used as model systems in this study.

16.
BMJ Open Sport Exerc Med ; 5(1): e000532, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31191976

RESUMO

Objectives: To assess the outcome of conservative treatment for chronic exertional compartment syndrome (CECS) as it relates to the reduction in surgical fasciotomy and return to active duty in a military population. Methods: Historic cohort. From 2015 to 2018, 75 surgically eligible patients with pressure-positive anterior CECS (Group 1), or with positive pressures and associated medial tibial stress syndrome (Group 2), underwent a conservative treatment programme emphasising gait retraining of running and marching. Treatment success was defined as return to duty, without surgery. Fifty patients from 2015 to 2017 were surveyed to assess mid-term outcomes. Results: The average duration of conservative treatment was 144.9 (±59.6) days. Initially, 65% (49/75) were able to return to duty; 28% (21/75) were referred for surgery and 7% (5/75) left the armed forces. There was no difference in outcomes between Group 1 and Group 2. Survey response rate, on average after 742 days (SD 267, range 381-1256), was 84% (42/50); 57% (24/42) had continued duty, without surgery; of them, 43% were at the same military specialty, 57% in a physically less demanding job. Conclusion: A conservative treatment programme for anterior CECS was able to return 65 % of patients to active duty, without surgery. At 2 years, the success rate decreased slightly, but remained positive at 57%. In this high-risk group, initiating a conservative treatment protocol with an emphasis on gait retraining can significantly reduce the need for surgical fasciotomy. For those that fail conservative treatment, surgical release may still be indicated.

17.
Acc Chem Res ; 52(5): 1400-1408, 2019 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31017760

RESUMO

Selective molecular ion probes are often insoluble in water and require a hydrophobic solvent environment for strong and selective binding, which runs counter to the desire of utilizing them in a homogeneous solution. This Account aims to guide the reader on how such molecules, often coined ionophores, can be harnessed to design exceptionally useful optical and electrochemical sensors. We start here with some historical context on the design of such ionophores and continue with the explanation of the response mechanism of optical and potentiometric sensors and the role of combined components to build a robust ion sensor. This Account is addressed to nonspecialist readers and for this reason avoids extensive use of equations or theoretical considerations. The interested reader should turn to the original literature for further reading. Emulsified optical sensors are introduced as an initial example. Here, multiple reagents are confined in an attoliter sensing nanodroplet of the organic phase, immiscible with the aqueous sample phase. In this case, the ionophore molecules may retain their high affinity and selectivity to the target ion and the aqueous sample phase does not have to be modified. Emulsified optical sensors allow one to achieve the selective chemical sensing of ions, even with optically silent ionophores. Such ionophore-based nanodroplets are also discussed as a useful novel class of complexometric titration reagents and optical end point indicators with unique selectivities. We then turn our attention to potentiometric sensing probes and briefly discuss the unique opportunity of a direct characterization of ion-ionophore complexation properties offered by membrane electrodes. A carbonate-selective membrane electrode containing a highly selective tweezer-type ionophore with trifluoroacetophenone functional groups is then used as an example for the construction of a robust all-solid-state sensor. This potentiometric probe, in combination with a pH electrode, can directly measure PCO2 in freshwater lakes, demonstrating a dramatically improved response time relative to traditional sensors equipped with a gas-permeable membrane. In recent years, new sensing modes and electrode designs have been introduced to expand the application scope of ionophore-based potentiometric sensors. Membrane electrodes containing ionophores are placed under dynamic electrochemistry control to give important progress in the field. We specifically highlight our recent works by membranes that are controlled by chronopotentiometry (controlled current) for speciation analysis, by ion transfer voltammetry on thin sensing films for multianalyte detection, by exhaustive coulometry for potentially calibration-free sensors and with coulometric membrane pumps for the selective delivery of reagents.

18.
ACS Sens ; 4(4): 1008-1016, 2019 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-30859814

RESUMO

We show here that the response of ion-selective membrane electrodes (ISEs) based on traditional PVC membranes can be directly translated to a colorimetric readout by a closed bipolar electrode (BPE) arrangement. Because the resulting optical response is based on the turnover of the redox probe, ferroin, dissolved in a thin layer compartment, it directly indicates the potential change at the ISE in combination with a reference electrode. This class of probes measures ion activity, analogous to their ISE counterparts. Unlike other ion optodes, the response is also fully tunable over a wide concentration range by the application of an external potential and occurs in a compartment that is physically separate from the sample. To allow for the electrical charge to pass across the ion-selective electrodes, the membranes are doped with inert lipophilic electrolyte, ETH 500, but otherwise have an established composition. The observed response behavior correlates well with theory. A wide range of ion-selective membranes are confirmed to work with this readout principle, demonstrating the detection of potassium, sodium, calcium, and carbonate ions. The corresponding sigmodal calibration curve is used for quantitative analysis in a range of samples including commercial beverages and river and lake samples. The data are successfully correlated with atomic emission spectroscopy and direct potentiometry.

19.
Anal Chem ; 91(7): 4889-4895, 2019 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-30835441

RESUMO

We introduce here a general strategy to read out chronopotentiometric sensors by electrogenerated chemiluminescence (ECL). The potentials generated in chronopotentiometry in a sample compartment are used to control the ECL in a separate detection compartment. A three-electrode cell is used to monitor the concentration changes of the analyte, while the luminol-H2O2 system is responsible for ECL. The principle was shown to be feasible by theoretical simulations, indicating that the sampled times at a chosen potential, rather than traditional transition times, similarly give linear behavior between concentration and the square root of sampled time. With the help of a voltage adapter, the experimental combination between chronopotentiometry and ECL was successfully implemented. As an initial proof of concept, the ferro/ferricyanide redox couple was investigated. The square root of time giving maximum light output changed linearly with ferrocyanide concentration in the range from 0.70 to 4.81 mM. The method was successfully applied to the visual detection of carbonate alkalinity from 0.06 to 0.62 mM using chronopotentiometry at an ionophore-based hydrogen ion-selective membrane electrode. The measurements of carbonate in real samples including river water and commercial mineral water were successfully demonstrated.

20.
ACS Sens ; 4(3): 670-677, 2019 03 22.
Artigo em Inglês | MEDLINE | ID: mdl-30702271

RESUMO

A distance-based analysis of potassium ion (K+) is introduced that is performed on a microfluidic paper-based analytical device (µPAD) coupled to an ion-selective capillary sensor. The concept is based on two sequential steps, the selective replacement of analyte ion with an ionic dye, and the detection of this dye in a distance-based readout on paper. To achieve the first step, the capillary sensor holds a poly(vinyl chloride) (PVC) membrane film layer plasticized by dioctyl sebacate (DOS) that contains the potassium ionophore valinomycin, a lipophilic cation-exchanger and the ionic indicator Thioflavin T (ThT) on its inner wall. Upon introduction of the sample, K+ in the aqueous sample solution is quantitatively extracted into the film membrane and replaced with ThT. To convert the ion exchange signal into a distance-based analysis, this solution was dropped onto the inlet area of a µPAD to flow the ThT along a channel defined by wax printing, resulting in the electrostatic binding of ThT to the cellulose carboxylic groups. The initial amount of K+ determines the amount of ThT in the aqueous solution after ion-exchange, and consequently the distance of ThT-colored area reflects the sample K+ concentration. The ion exchange reaction was operated in a so-called "exhaustive sensing mode" and gave a distinct response in a narrow range of K+ concentration (1-6 mM) that cannot be achieved by the classical optode sensing mode. The absence of hydrogen ions from the equilibrium competition of the capillary sensor contributed to a complete pH-independence, unlike conventional optodes that contain a pH sensitive indicator. A very high selectivity for K+ over Na+ and Ca2+ has been confirmed in separate solutions and mixed solutions tests. K+ measurements in pooled serum samples at concentrations between 2 and 6 mM are successfully demonstrated on a temperature controlled support.


Assuntos
Técnicas de Química Analítica/instrumentação , Corantes/química , Dispositivos Lab-On-A-Chip , Papel , Potássio/análise , Concentração de Íons de Hidrogênio , Limite de Detecção , Potássio/sangue , Potássio/química
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