579 research outputs found
Frequency-dependent spontaneous emission rate from CdSe and CdTe nanocrystals: influence of dark states
We studied the rate of spontaneous emission from colloidal CdSe and CdTe
nanocrystals at room temperature. The decay rate, obtained from luminescence
decay curves, increases with the emission frequency in a supra-linear way. This
dependence is explained by the thermal occupation of dark exciton states at
room temperature, giving rise to a strong attenuation of the rate of emission.
The supra-linear dependence is in agreement with the results of tight-binding
calculations.Comment: 11 page
The electron's dance
A joint Fermilab/SLAC publicationParis' Trocadéro science exhibition allows science enthusiasts to see--and even control--a real electron accelerator
Electrochemical DNA-sensor for evaluation of total antioxidant capacity of flavours and flavoured waters using superoxide radical damage
In this paper, a biosensor based on a glassy carbon electrode (GCE) was used for the evaluation of the total
antioxidant capacity (TAC) of flavours and flavoured waters. This biosensor was constructed by immobilising
purine bases, guanine and adenine, on a GCE. Square wave voltammetry (SWV) was selected for
the development of this methodology. Damage caused by the reactive oxygen species (ROS), superoxide
radical (O2·−), generated by the xanthine/xanthine oxidase (XOD) system on the DNA-biosensor was
evaluated. DNA-biosensor encountered with oxidative lesion when it was in contact with the O2·−. There
was less oxidative damage when reactive antioxidants were added. The antioxidants used in this work
were ascorbic acid, gallic acid, caffeic acid, coumaric acid and resveratrol. These antioxidants are capable
of scavenging the superoxide radical and therefore protect the purine bases immobilized on the GCE
surface. The results demonstrated that the DNA-based biosensor is suitable for the rapid assess of TAC in
beverages
Electrochemical evaluation of total antioxidant capacity of beverages using a purine-biosensor
In this paper, it was evaluated the total antioxidant capacity (TAC) of beverages using an electrochemical
biosensor. The biosensor consisted on the purine base (guanine or adenine) electro-immobilization on a
glassy carbon electrode surface (GCE). Purine base damage was induced by the hydroxyl radical generated
by Fenton-type reaction. Five antioxidants were applied to counteract the deleterious effects of
the hydroxyl radical. The antioxidants used were ascorbic acid, gallic acid, caffeic acid, coumaric acid
and resveratrol. These antioxidants have the ability to scavenger the hydroxyl radical and protect the
guanine and adenine immobilized on the GCE surface. The interaction carried out between the purinebase
immobilized and the free radical in the absence and presence of antioxidants was evaluated by
means of changes in the guanine and adenine anodic peak obtained by square wave voltammetry
(SWV). The results demonstrated that the purine-biosensors are suitable for rapid assessment of TAC
in beverages
Carbon surfaces for the oxidative quantification of pravastatin: glassy-carbon vs. screen-printed carbon electrodes
The electrooxidative behavior of pravastatin (PRV) in aqueous media was studied by square-wave voltammetry at a glassycarbon
electrode (GCE) and at a screen-printed carbon electrode (SPCE). Maximum peak current intensities in a pH 5.0 buffer were
obtained at +1.3 V vs. AgCl/Ag and +1.0 V vs. Ag for the GCE and SPCE surface respectively. Validation of the developed methodologies
revealed good performance characteristics and confirmed their applicability to the quantification of PRV in pharmaceutical
products, without significant sample pretreatment. A comparative analysis between the two electrode types showed that SPCEs are
preferred as an electrode surface because of their higher sensitivity and the elimination of the need to clean the electrode’s surface
for its renewal, which frequently is, if not always, the rate-limiting step in voltammetric analysis
Heterointerface effects on the charging energy of shallow D- ground state in silicon: the role of dielectric mismatch
Donor states in Si nanodevices can be strongly modified by nearby insulating
barriers and metallic gates. We report here experimental results indicating a
strong reduction in the charging energy of isolated As dopants in Si FinFETs
relative to the bulk value. By studying the problem of two electrons bound to a
shallow donor within the effective mass approach, we find that the measured
small charging energy may be due to a combined effect of the insulator
screening and the proximity of metallic gates.Comment: 7 pages, 6 figure
Direct electroanalytical determination of fluvastatin in a pharmaceutical dosage form: batch and flow analysis
The reduction of luvastatin (FLV) at a hanging mercury-drop electrode
(HMDE) was studied by square-wave adsorptive-stripping voltammetry
(SWAdSV). FLV can be accumulated and reduced at the electrode, with a
maximum peak current intensity at a potential of approximately 1.26V vs.
AgCl=Ag, in an aqueous electrolyte solution of pH 5.25. The method shows linearity
between peak current intensity and FLV concentration between 1.0 10 8
and 2.7 10 6 mol L 1. Limits of detection (LOD) and quantification (LOQ)
were found to be 9.9 10 9 mol L 1 and 3.3 10 8 mol L 1, respectively.
Furthermore, FLV oxidation at a glassy carbon electrode surface was used
for its hydrodynamic monitoring by amperometric detection in a flow-injection
system. The amperometric signal was linear with FLV concentration over the
range 1.0 10 6 to 1.0 10 5 mol L 1, with an LOD of 2.4 10 7 mol L 1
and an LOQ of 8.0 10 7 mol L 1. A sample rate of 50 injections per hour
was achieved.
Both methods were validated and showed to be precise and accurate, being
satisfactorily applied to the determination of FLV in a commercial pharmaceutical
Adsorptive stripping voltammetric determination of venlafaxine in urine with a mercury film microelectrode
An adsorptive stripping voltammetric procedure for the determination
of the antidepressant venlafaxine in urine using a mercury film
microelectrode wasdeveloped. The method is based on controlled
adsorptive accumulation of the drug at the potential of 1.00V (vs.
Ag/AgCl) in the presence of 1.25 x10 -2 molL- 1 borate buffer (pH
8.7). Urine samples were analyzed directly after performing a
ten-fold dilution with the supporting electrolyte but without other pretreatment. The limit of detection obtained for a 30 s collection
time was 0.693x 10- 6 mol L -1. Recovery experimentsgave good
results at the 10 -6 mol L- 1 level (bias less 5% were obtained)
Electroanalysis of urinary L-dopa using tyrosinase immobilized on gold nanoelectrode ensembles
The performance of an amperometric biosensor constructed by associating tyrosinase (Tyr) enzyme with the advantages of a 3D gold nanoelectrode ensemble (GNEE) is evaluated in a flow-injection analysis (FIA) system for the analysis of l-dopa. GNEEs were fabricated by electroless deposition of the metal within the pores of polycarbonate track-etched membranes. A simple solvent etching procedure based on the solubility of polycarbonate membranes is adopted for the fabrication of the 3D GNEE. Afterward, enzyme was immobilized onto preformed self-assembled monolayers of cysteamine on the 3D GNEEs (GNEE-Tyr) via cross-linking with glutaraldehyde. The experimental conditions of the FIA system, such as the detection potential (−0.200 V vs. Ag/AgCl) and flow rates (1.0 mL min−1) were optimized. Analytical responses for l-dopa were obtained in a wide concentration range between 1 × 10−8 mol L−1 and 1 × 10−2 mol L−1. The limit of quantification was found to be 1 × 10−8 mol L−1 with a resultant % RSD of 7.23% (n = 5). The limit of detection was found to be 1 × 10−9 mol L−1 (S/N = 3). The common interfering compounds, namely glucose (10 mmol L−1), ascorbic acid (10 mmol L−1), and urea (10 mmol L−1), were studied. The recovery of l-dopa (1 × 10−7 mol L−1) from spiked urine samples was found to be 96%. Therefore, the developed method is adequate to be applied in the clinical analysis
High-performance electrochemical immunomagnetic assay for breast cancer analysis
Despite the evolution of targeted therapies in oncology, some challenges such as screening and early diagnosis of cancer-related biomarkers still remain. The analysis of the Human Epidermal growth factor Receptor 2 (HER2) in biological fluids provides essential information for effective treatments. In this work we report the development of an electrochemical immunomagnetic bioassay for the analysis of the extracellular domain of HER2 (HER2-ECD) in human serum and cancer cells. Biomodified carboxylic acid functionalized magnetic beads (COOH-MBs) were used as the capture probe and an antibody labelled with alkaline phosphatase (AP) as the signalling probe. In the presence of HER2-ECD a sandwich complex was formed on the MBs, which were magnetically attracted to the surface of a screen-printed carbon electrode (SPCE). After the addition of 3-indoxyl phosphate and silver ions, used as the enzymatic substrate, the immunological interaction was detected by linear sweep voltammetry. Two linear concentration ranges were established: one between 5.0 and 50 ng/mL and another between 50 and 100 ng/mL. The developed assay provided a clinically useful detection limit (2.8 ng/mL) and has an adequate precision (Vx0 < 5%). The assay provided accurate results and was selective towards the target biomarker. Additionally, CTCs were analysed in human serum and a detection limit of 3 cells/mL was achieved for the HER+ breast cancer cell line SK-BR-3.The authors are grateful for the financial support from the Fundação para a Ciência e a
Tecnologia (FCT) / the Ministério da Ciência, Tecnologia e Ensino Superior (MCTES) through
national funds (Portugal) (LAQV - UID/QUI/50006/2019 and CINTESIS - UID/IC/4255/2019).
Maria Freitas is grateful to FCT for her PhD grant (SFRH/BD/111942/2015), financed by POPH-
QREN-Tipologia 4.1-Formação Avançada, subsidized by Fundo Social Europeu and the MCTES.
The authors are also thankful to Rui Rocha and CEMUP “Centro de Materiais da Universidade
do Porto” for the SEM workinfo:eu-repo/semantics/publishedVersio
- …