Papers by Araceli González
Talanta, 1995
A new electrochemical biosensor was developed by incorporating an enzyme into a solid-paraffingra... more A new electrochemical biosensor was developed by incorporating an enzyme into a solid-paraffingraphite-particle matrix. Tyrosinase served as model enzyme and the biosensor response was characterized with respect to its response to dopamine. The influence of different experimental parameters (tyrosinase loading, flow rate, oxygen dependence, pH, etc.) was investigated in order to optimize the biosensor performance. The electrode response was fast, reversible and linear in a large concentration domain (0.1 pM-I mM). The enzyme-solid paraffin carbon paste electrode (CPE) showed markedly improved stability in flow injection analysis compared to the classical liquid paraffin-graphite-based biosensors. The biosensor allowed a sampling rate of 79 samples per hour, the repeatability of the injections was improved with respect to the classical CPE with a relative standard deviation of 2.2% (N--63), and the detection limit for dopamine was 50 riM. The biosensor response to some phenol and catechol derivatives was also investigated.
Serum leptin levels in women with systemic lupus erythematosus
Rheumatology International, 2002
The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SL... more The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SLE). Forty-one women with SLE were compared with 23 healthy women of similar age and body mass index (BMI). Clinical characteristics and Mexican systemic lupus erythematosus disease activity index (Mex-SLEDAI) score were assessed. Serum leptin levels (ng/dl) were measured by enzyme-linked immunosorbent assay (ELISA). Comparisons of leptin levels were made with the Mann-Whitney U-test. In a multiple regression analysis, those factors that could influence the leptin levels were adjusted. Patients with SLE had higher leptin levels than the control group (SLE median 31 vs control median 15, P=0.023). After adjusting by other variables, the serum leptin levels remained higher in SLE than in controls (P=0.02). Patients with SLE had no association between leptin levels and Mex-SLEDAI score, age, duration of disease, or prednisone doses. Those with SLE had higher leptin levels than controls. Further longitudinal studies are required to evaluate the role of this hormone in the exacerbations of SLE.
Clinical Rheumatology, 2008
This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and system... more This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) from underserved healthcare settings. We conducted a cross-sectional survey of 102 ethnically diverse patients—70 with RA and 32 with SLE—attending rheumatology clinics at publicly funded hospitals in Houston, Texas; 43% were Hispanic, 32% African-American, and 25% White. Treatment adherence was evaluated using the compliance questionnaire rheumatology (CQR; 0, low adherence and 100, high adherence) and the questionnaire of the Adult AIDS Clinical Trials Group (AACTG). The patients were also asked how often they forgot to take their prescribed medications or discontinued them on their own. Mean patient age was 48.5 years; 75% were female, 32% were African-American, 43% Hispanic, and 25% White. Only one third reported never forgetting to take their medications; 40% reported having stopped their medications on their own because of side effects, and 20% because of lack of efficacy. Mean CQR score was 69.1 ± 10.5, suggesting moderate adherence overall. Differences were also observed across ethnic groups: 23% of ethnic minority patients had problems taking their medications at specified times compared to 11% of Whites (p = 0.03). Lower education and side effects were associated with lower adherence. No differences were observed between RA and SLE patients. Many patients with RA and SLE report problems with treatment adherence. These appear to be more prevalent in African Americans and Hispanics than Whites; the impact of decreased adherence on outcomes could be significant and should be considered when treating patients with RA and SLE.
Serum leptin levels in women with systemic lupus erythematosus
Rheumatology International, 2002
The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SL... more The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SLE). Forty-one women with SLE were compared with 23 healthy women of similar age and body mass index (BMI). Clinical characteristics and Mexican systemic lupus erythematosus disease activity index (Mex-SLEDAI) score were assessed. Serum leptin levels (ng/dl) were measured by enzyme-linked immunosorbent assay (ELISA). Comparisons of leptin levels were made with the Mann-Whitney U-test. In a multiple regression analysis, those factors that could influence the leptin levels were adjusted. Patients with SLE had higher leptin levels than the control group (SLE median 31 vs control median 15, P=0.023). After adjusting by other variables, the serum leptin levels remained higher in SLE than in controls (P=0.02). Patients with SLE had no association between leptin levels and Mex-SLEDAI score, age, duration of disease, or prednisone doses. Those with SLE had higher leptin levels than controls. Further longitudinal studies are required to evaluate the role of this hormone in the exacerbations of SLE.
Clinical Rheumatology, 2008
This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and system... more This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) from underserved healthcare settings. We conducted a cross-sectional survey of 102 ethnically diverse patients—70 with RA and 32 with SLE—attending rheumatology clinics at publicly funded hospitals in Houston, Texas; 43% were Hispanic, 32% African-American, and 25% White. Treatment adherence was evaluated using the compliance questionnaire rheumatology (CQR; 0, low adherence and 100, high adherence) and the questionnaire of the Adult AIDS Clinical Trials Group (AACTG). The patients were also asked how often they forgot to take their prescribed medications or discontinued them on their own. Mean patient age was 48.5 years; 75% were female, 32% were African-American, 43% Hispanic, and 25% White. Only one third reported never forgetting to take their medications; 40% reported having stopped their medications on their own because of side effects, and 20% because of lack of efficacy. Mean CQR score was 69.1 ± 10.5, suggesting moderate adherence overall. Differences were also observed across ethnic groups: 23% of ethnic minority patients had problems taking their medications at specified times compared to 11% of Whites (p = 0.03). Lower education and side effects were associated with lower adherence. No differences were observed between RA and SLE patients. Many patients with RA and SLE report problems with treatment adherence. These appear to be more prevalent in African Americans and Hispanics than Whites; the impact of decreased adherence on outcomes could be significant and should be considered when treating patients with RA and SLE.
Serum leptin levels in women with systemic lupus erythematosus
Rheumatology International, 2002
The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SL... more The purpose of this study was to evaluate serum leptin levels in systemic lupus erythematosus (SLE). Forty-one women with SLE were compared with 23 healthy women of similar age and body mass index (BMI). Clinical characteristics and Mexican systemic lupus erythematosus disease activity index (Mex-SLEDAI) score were assessed. Serum leptin levels (ng/dl) were measured by enzyme-linked immunosorbent assay (ELISA). Comparisons of leptin levels were made with the Mann-Whitney U-test. In a multiple regression analysis, those factors that could influence the leptin levels were adjusted. Patients with SLE had higher leptin levels than the control group (SLE median 31 vs control median 15, P=0.023). After adjusting by other variables, the serum leptin levels remained higher in SLE than in controls (P=0.02). Patients with SLE had no association between leptin levels and Mex-SLEDAI score, age, duration of disease, or prednisone doses. Those with SLE had higher leptin levels than controls. Further longitudinal studies are required to evaluate the role of this hormone in the exacerbations of SLE.
Clinical Rheumatology, 2008
This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and system... more This study assessed self-reported adherence in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) from underserved healthcare settings. We conducted a cross-sectional survey of 102 ethnically diverse patients—70 with RA and 32 with SLE—attending rheumatology clinics at publicly funded hospitals in Houston, Texas; 43% were Hispanic, 32% African-American, and 25% White. Treatment adherence was evaluated using the compliance questionnaire rheumatology (CQR; 0, low adherence and 100, high adherence) and the questionnaire of the Adult AIDS Clinical Trials Group (AACTG). The patients were also asked how often they forgot to take their prescribed medications or discontinued them on their own. Mean patient age was 48.5 years; 75% were female, 32% were African-American, 43% Hispanic, and 25% White. Only one third reported never forgetting to take their medications; 40% reported having stopped their medications on their own because of side effects, and 20% because of lack of efficacy. Mean CQR score was 69.1 ± 10.5, suggesting moderate adherence overall. Differences were also observed across ethnic groups: 23% of ethnic minority patients had problems taking their medications at specified times compared to 11% of Whites (p = 0.03). Lower education and side effects were associated with lower adherence. No differences were observed between RA and SLE patients. Many patients with RA and SLE report problems with treatment adherence. These appear to be more prevalent in African Americans and Hispanics than Whites; the impact of decreased adherence on outcomes could be significant and should be considered when treating patients with RA and SLE.
Journal of Organic Chemistry, 1992
Novel7r-extended thiophene-fused TCNQ-type and DCNQI-type acceptors have been synthesized from th... more Novel7r-extended thiophene-fused TCNQ-type and DCNQI-type acceptors have been synthesized from the corr~?onding quinones by reaction with Lehnert's reagent and bi.s(trimethylsilyl)carbodiimide (ETC), respectively. Addltlonaliy, an example of the little-known hybrid TCNQ-DCNQI-type acceptor has also been obtained. The cyclic voltammetric data of the novel acceptors reveal two different behaviors for these molecules. The TCNQ-type derivatives exhibit a two-electron single-wave reduction to the dianion, as confirmed by controlled potential coulometry analysis. The DCNQI-type derivatives display two reduction waves to the corresponding radical anion and dianion. The same behavior is shown by the hybrid TCNQ-DCNQI derivative. The acceptor ability i.s related to molecular planarity, and a comparative crystallographic study involving TCNQ-type and DCNQI-type derivatives (6a, 7a, and 8a) has been performed.
Electrochimica Acta, 2008
The unique properties of gold nanoparticles to provide a suitable microenvironment for biomolecul... more The unique properties of gold nanoparticles to provide a suitable microenvironment for biomolecules immobilization retaining their biological activity, and to facilitate electron transfer between the immobilized proteins and electrode surfaces, have led to an intensive use of this nanomaterial for the construction of electrochemical biosensors with enhanced analytical performance with respect to other biosensor designs. Recent advances in this field are reviewed in this article. The advantageous operational characteristics of the biosensing devices designed making use of gold nanoparticles are highlighted with respect to non-nanostructured biosensors and some illustrative examples are commented. Electrochemical enzyme biosensors including those using hybrid materials with carbon nanotubes and polymers, sol-gel matrices, and layer-by-layer architectures are considered. Moreover, electrochemical immunosensors in which gold nanoparticles play a crucial role in the electrode transduction enhancement of the affinity reaction as well as in the efficiency of immunoreagents immobilization in a stable mode are reviewed. Similarly, recent advances in the development of DNA biosensors using gold nanoparticles to improve DNA immobilization on electrode surfaces and as suitable labels to improve detection of hybridization events are considered. Finally, other biosensors designed with gold nanoparticles oriented to electrically contact redox enzymes to electrodes by a reconstitution process and to the study of direct electron transfer between redox proteins and electrode surfaces have also been treated.
Biosensors & Bioelectronics, 2006
The design of a new tyrosinase biosensor with improved stability and sensitivity is reported. The... more The design of a new tyrosinase biosensor with improved stability and sensitivity is reported. The biosensor design is based on the construction of a graphite-Teflon composite electrode matrix in which the enzyme and colloidal gold nanoparticles are incorporated by simple physical inclusion. Experimental variables such as the colloidal gold loading into the composite matrix, the enzyme loading and the potential applied to the bioelectrode were optimized. The Tyr-Au coll -graphite-Teflon biosensor exhibited suitable amperometric responses at −0.10 V for the different phenolic compounds tested and 4-methylphenol). The limits of detection obtained were 3 nM for catechol, 3.3 M for 4-chloro-2-methylphenol, and approximately 20 nM for the rest of phenolic compounds. The presence of colloidal gold into the composite matrix gives rise to enhanced kinetics of both the enzyme reaction and the electrochemical reduction of the corresponding o-quinones at the electrode surface, thus allowing the achievement of a high sensitivity. The biosensor exhibited an excellent renewability by simple polishing, with a lifetime of at least 39 days without apparent loss of the immobilized enzyme activity. The usefulness of the biosensor for the analysis of real samples was evaluated by performing the estimation of the content of phenolic compounds in water samples of different characteristics.
Analytica Chimica Acta, 2001
The electroanalytical capabilities of cylindrical carbon fibre microelectrodes (CFMEs) modified w... more The electroanalytical capabilities of cylindrical carbon fibre microelectrodes (CFMEs) modified with electrodeposited rhodium for their use as amperometric microsensors in the detection of hydrazine under flow-injection conditions are discussed. Metallized CFMEs were prepared potentiostatically at −0.80 V in an acetate buffer solution of pH 4.5 containing 100 mg l −1 Rh(III), and characterised by cyclic voltammetry. Rh-CFMEs showed electrocatalytic ability towards the oxidation of hydrazine and some other organic compounds. A good stability of the metallised microelectrodes was found when they were used for the amperometric detection of hydrazine under flowing conditions, with no need to regenerate the electrode surface. Moreover, the signal-to-noise ratio was remarkably better at the Rh-CFME than at a Rh-modified glassy carbon electrode of conventional size. A limit of detection of 6.2 × 10 −7 mol l −1 hydrazine (approximately 20 g l −1 ) was obtained.
Talanta, 2007
A simple and sensitive electroanalytical method was developed to determine the Endocrine Disrupti... more A simple and sensitive electroanalytical method was developed to determine the Endocrine Disrupting chemical 4-tert-octylphenol on clay modified carbon paste electrode (Clay/CPE). The electrochemical response of the proposed electrode was studied by means of cyclic and square wave voltammetry. It has found that the oxidation of 4-tert-octylphenol on the clay/CPE displayed a well-defined oxidation peak. Under these optimal conditions, a linear relation between concentrations of 4-tert-octylphenol current response was obtained over range of 7.26×10 −6 to 3.87×10 −7 with a detection and quantification limit of 9.2 ×10 -7 M and 3.06×10 -6 M, respectively. The correlation coefficient is 0.9963. The modified electrode showed suitable sensitivity, high stability and an accurate detection of 4-tert-octylphenol.The modified electrode also relevant suitable selectivity for various phenolic estrogenic compounds.
Analytical and Bioanalytical Chemistry, 2007
The voltammetric behaviour and amperometric detection of tetracycline (TC) antibiotics at multi-w... more The voltammetric behaviour and amperometric detection of tetracycline (TC) antibiotics at multi-wall carbon nanotube modified glassy carbon electrodes (MWCNT-GCE) are reported. Cyclic voltammograms of TCs showed enhanced oxidation responses at the MWCNT-GCE with respect to the bare GCE, attributable to the increased active electrode surface area. Hydrodynamic voltammograms obtained by flow-injection with amperometric detection at the MWCNT-GCE led us to select a potential value E det = +1.20 V. The repeatability of the amperometric responses was much better than that achieved with bare GCE (RSD ranged from 7 to 12%), with RSD values for i p of around 3%, thus demonstrating the antifouling capability of MWCNT modified electrodes. An HPLC method with amperometric electrochemical detection (ED) at the MWCNT-GCE was developed for tetracycline, oxytetracycline (OTC), chlortetracycline and doxycycline (DC). A mobile phase consisting of 18:82 acetonitrile/0.05 mol L−1 phosphate buffer of pH 2.5 was selected. The limits of detection ranged from 0.09 μmol L−1 for OTC to 0.44 μmol L−1 for DC. The possibility to carry out multiresidue analysis is demonstrated. The HPLC-ED/MWCNT-GCE method was applied to the analysis of fish farm pool water and underground well water samples spiked with the four TCs at 2.0 × 10−7 mol L−1. Solid-phase extraction was accomplished for the preconcentration of the analytes and clean-up of the samples. Recoveries ranged from 87 ± 6 to 99 ± 3%. Under preconcentration conditions, limits of detection in the water samples were between 0.50 and 3.10 ng mL−1.
Electroanalysis, 1998
The voltammetric and flow-injection amperometric behaviors of several substances used as antioxid... more The voltammetric and flow-injection amperometric behaviors of several substances used as antioxidants in the food and pharmaceutical industries at carbon paste electrodes, with paraffin as binding agent, and at graphite-40 % PTFE composite electrodes were compared on the basis of the different hydrophobicity of the antioxidants. Aqueous solutions, alcohol-water mixtures and oil-in-water-emulsions were used as working media. No voltammetric or flow-injection responses were obtained for high hydrophobic antioxidants (BHT, Irganox-1076 and Irganox-1010) at graphite-PTFE electrodes. On the contrary, carbon paste electrodes allowed the attainment of analytically useful signals for these compounds. A pulse amperometric detection (PAD) scheme should be applied in these cases for the cleaning of the electrode surface. The use of graphite-PTFE electrodes seems to be advantageous for the less hydrophobic antioxidants such us propyl gallate and TBHQ. An adsorption process for PG and a faster electrode kinetic in the case of TBHQ were shown to occur by cyclic voltammetry at the PTFE composite electrode. Furthermore, this electrode allows the use of lower potentials for the amperometric detection of these compounds than the carbon paste electrode. Good reproducibility of the successive amperometric responses was also observed. The mutual influence of the electrode surface composition and the lipophilic characteristics of the molecules tested is discussed.
Analytica Chimica Acta, 2005
The preparation of a tyrosinase biosensor based on the immobilization of the enzyme onto a glassy... more The preparation of a tyrosinase biosensor based on the immobilization of the enzyme onto a glassy carbon electrode modified with electrodeposited gold nanoparticles (Tyr-nAu-GCE) is reported. The enzyme immobilized by cross-linking with glutaraldehyde retains a high bioactivity on this electrode material. Under the optimized working variables (a Au electrodeposition potential of −200 mV for 60 s, an enzyme loading of 457 U, a detection potential of −0.10 V and a 0.1 mol l −1 phosphate buffer solution of pH 7.4 as working medium) the biosensor exhibited a rapid response to the changes in the substrate concentration for all the phenolic compounds tested: phenol, catechol, caffeic acid, chlorogenic acid, gallic acid and protocatechualdehyde. A R.S.D. of 3.6% (n = 6) was obtained from the slope values of successive calibration plots for catechol with the same Tyr-nAu-GCE with no need to apply a cleaning procedure to the biosensor. The useful lifetime of one single biosensor was of at least 18 days, and a R.S.D. of 4.8% was obtained for the slope values of catechol calibration plots obtained with five different biosensors. The kinetic constants and the analytical characteristics were calculated for all the phenolic compounds tested. The Tyr-nAu-GCE was applied for the estimation of the phenolic compounds content in red and white wines. A good correlation of the results (r = 0.990) was found when they were plotted versus those obtained by using the spectrophotometric method involving the Folin-Ciocalteau reagent.
Analytica Chimica Acta, 1999
The electrochemical behavior of cylindrical carbon ®ber microelectrodes (CFMEs), 8 mm in length, ... more The electrochemical behavior of cylindrical carbon ®ber microelectrodes (CFMEs), 8 mm in length, has been tested in lowpermitivity organic solvents such as toluene and ethyl acetate. Near-to-ideal steady-state responses were obtained by cyclic voltammetry for ferrocene solutions in these media, using low potential scan rates and a relatively high concentration of background electrolyte. A good adjustment of the voltammetric responses to that predicted by the theory was found in both solvents. Well-de®ned oxidation peaks were also obtained by differential-pulse and square wave voltammetry. Square-wave voltammetry (SWV) in ethyl acetate has been used to develop a method for the determination of the food additive vanillin. A linear calibration graph was obtained in the 1.0Â10 À5 to 7.0Â10 À4 mol l À1 concentration range with a slope of (7.1AE0.1)Â10 3 mA l mol À1 . A limit of detection of 4.2Â10 À6 mol l À1 vanillin, and a relative standard deviation of 2.0% for a concentration level of 5.0Â10 À4 mol l À1 (n10) were obtained. The SWV method was applied to the determination of vanillin in dehydrated pudding powder. This determination was performed directly in the samples extract in ethyl acetate. The obtained results were statistically compared with those provided by a reference spectrophotometric method, and no signi®cant differences between both methods were found. # 0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. P I I : S 0 0 0 3 -2 6 7 0 ( 9 8 ) 0 0 6 4 3 -6
Analytica Chimica Acta, 1999
The use of cylindrical carbon fiber microelectrodes (CFMEs) modified with poly(3-methylthiophene)... more The use of cylindrical carbon fiber microelectrodes (CFMEs) modified with poly(3-methylthiophene) (P3MT) films as amperometric microsensors for continuous monitoring of some amino acids such as tyrosine (Tyr), tryptophan (Trp), L-dopa, and related compounds such as tyramine and ascorbic acid, as well as small peptides such as Trp-Ala and Tyr-Gly, is discussed. Important practical advantages with respect to conventional glassy carbon (GC) electrodes, and also with respect to P3MT-coated GC electrodes of conventional size are demonstrated. The electrocatalytic ability of the modified surface allows the possibility of applying moderate potentials for the amperometric detection of the above mentioned compounds. Flow-injection experiments carried out using a phosphate buffer solution of pH 7.0 as the carrier, and an applied potential of +0.8 V showed that no cleaning or regeneration pretreatment was needed when working with the same polymer modified electrode during the whole working day. The effect of the presence of acetonitrile or methanol in the flowing solution was evaluated. A flow-injection method with amperometric detection was developed for the determination of L-dopa in pharmaceutical preparations. Finally, the modified microelectrodes have also shown suitable for amperometric detection in liquid chromatography (LC). A mobile phase composed of 5 : 95 (v/v) methanol : phosphate buffer solution of pH 7.0 allowed a good separation of mixtures of ascorbic acid, L-dopa, Tyr, tyramine and Trp, with detection limits of around 160 pmol. Furthermore, the possibility of detection of Tyr-and Trp-containing oligopeptides was also demonstrated. (J.M. Pingarrón) 0003-2670/99/$ -see front matter ©1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 0 3 -2 6 7 0 ( 9 9 ) 0 0 5 0 7 -3
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Papers by Araceli González