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World Congress on Biosensors 2014
Biosensors 2014
Tuesday 12 February 2013
Just Published: Analytica Chimica Acta
A new issue of this journal has just
been published. To see abstracts of the papers it contains (with links through
to the full papers) click here:
Nuclear Magnetic
Resonance (NMR) Spectroscopy has been extensively used for the analysis of olive
oil and it has been established as a valuable tool for its quality assessment
and authenticity. To date, a large number of research and review articles have
been published with regards to the analysis of olive oil reflecting the
potential of the NMR technique in these studies. In this critical review, we
cover recent results in the field and discuss deficiencies and precautions of
the three NMR techniques (1H, 13C, 31P) used
for the analysis of olive oil. The two methodological approaches of
metabonomics, metabolic profiling and metabolic fingerprinting, and the
statistical methods applied for the classification of olive oils will be
discussed in critical way. Some useful information about sample preparation, the
required instrumentation for an effective analysis, the experimental conditions
and data processing for obtaining high quality spectra will be presented as
well. Finally, a constructive criticism will be exercised on the present
methodologies used for the quality control and authentication of olive oil.
Graphical abstract
Highlights
► Overview of olive oil
analysis by 1H, 13C, and 31P NMR spectroscopy.
► Sample preparation. ► Experimental conditions and processing for metabonomic
analysis. ► Multivariate statistical methods for NMR data analysis. ► Quality
assessment and authentication of extra virgin olive oil.
Multivariate
curve resolution (MCR) is a widespread methodology for the analysis of process
data in many different application fields. This article intends to propose a
critical review of the recently published works. Particular attention will be
paid to situations requiring advanced and tailored applications of multivariate
curve resolution, dealing with improvements in preprocessing methods, multi-set
data arrangements, tailored constraints, issues related to non-ideal noise
structure and deviation to linearity. These analytical issues are tackling the
limits of applicability of MCR methods and, therefore, they can be considered as
the most challenging ones.
Graphical abstract
Highlights
► MCR is nowadays a
well-established and widespread methodology for mixture analysis. ► The
analytical issues requiring advanced applications of MCR are reviewed. ►
Attention is paid to the literature published the years
2008–2012.
Thin films
loaded with the drug paracetamol were produced from polymer blends formed by
hydroxypropylmethylcellulose (HPMC), polyvinylpyrrolidone (PVP) and
polyethyleneglycol (PEG), at various mass ratios of polymers and drug defined by
a d-optimal experimental design. NIR hyperspectral images were obtained from
each thin film formulation and the pixel-to-pixel quantification of the
constituents were carried out by partial least square (PLS) and multivariate
curve resolution–alternating least square (MCR-ALS) with three different
calibration/validation strategies. These strategies differ in the way to
construct the calibration and validation matrices and they had to be carried out
to suppress the bias on the quantification of the constituents in the polymer
blend. The errors of prediction in the models from MCR-ALS were influenced by
the calibration/validation strategy employed, but they were similar to the ones
from PLS model. Concentration distribution maps were built after pixel-to-pixel
predictions and their characteristics were analyzed.
Graphical abstract
Highlights
► NIR chemical imaging
and chemometrics were used for studying thin films based drug delivery systems.
► Thin films were polymers mixtures of HPMC, PVP and PEG-400 loaded with the
drug paracetamol. ► MCR-ALS provided initial biased results on quantification of
polymers and additional calibration step was required. ► Three different
strategies were tested to suppress the bias on the quantification by MCR-ALS. ►
Parcetamol distribution in the thin films has direct correlation with the PVP
and PEG, but inverse correlation with HPMC.
Self Organising
Maps (SOMs) are one of the most powerful learning strategies among neural
networks algorithms. SOMs have several adaptable parameters and the selection of
appropriate network architectures is required in order to make accurate
predictions. The major disadvantage of SOMs is probably due to the network
optimisation, since this procedure can be often time-expensive. Effects of
network size, training epochs and learning rate on the classification
performance of SOMs are known, whereas the effect of other parameters (type of
SOMs, weights initialisation, training algorithm, topology and boundary
conditions) are not so obvious. This study was addressed to analyse the effect
of SOMs parameters on the network classification performance, as well as on
their computational times, taking into consideration a significant number of
real datasets, in order to achieve a comprehensive statistical comparison.
Parameters were contemporaneously evaluated by means of an approach based on the
design of experiments, which enabled the investigation of their interaction
effects. Results highlighted the most important parameters which influence the
classification performance and enabled the identification of the optimal
settings, as well as the optimal architectures to reduce the computational time
of SOMs.
Graphical abstract
Highlights
► We evaluated effects
of SOMs parameters on classification and computational time. ► The study was
conducted on eighteen real datasets. ► Significant parameters and their
interactions on classification were highlighted. ► Optimal architectures to
reduce the computational time of SOMs was proposed.
Electrochemical
behavior of three antioxidants: butylated hydroxyanisole (BHA), butylated
hydroxytoluene (BHT) and butylated hydroquinone (TBHQ), was investigated at a
glassy carbon electrode modified with gold nanoparticles (AuNPs/GCE). This
electrode was characterized by scanning electron microscopy (SEM). The
experimental results indicated that the modified electrode was strongly
electroactive during the redox reactions of BHA, BHT and TBHQ, and this was
confirmed by the observed increased redox peak currents and shifted potentials;
in addition, the oxidation products of BHA and TBHQ were found to be the same.
The experimental conditions were optimized and the oxidation peaks of BHA and
BHT were clearly separated. Based on this, an electrochemical method was
researched and developed for the simultaneous determination of BHA, BHT and TBHQ
in mixtures with the use of first derivative voltammetry; the linear
concentration ranges were 0.10–1.50μgmL−1, 0.20–2.20μgmL−1
and 0.20–2.80μgmL−1, and detection limits were 0.039, 0.080 and
0.079μgmL−1, for BHA, BHT and TBHQ, respectively. The proposed method
was successfully applied for the analysis of the three analytes in edible oil
samples.
Graphical abstract
Highlights
► A gold nanoparticles
modified glassy carbon electrode (AuNPs/GCE) was constructed. ► The
electrochemical mechanism of BHA, BHT and TBHQ at the AuNPs/GCE was studied. ►
The oxidation products of BHA and TBHQ were found to be the same. ►
First-derivative method was used to resolve the overlapped voltammograms. ►
Synthetic antioxidants in food samples were analyzed.
A novel
electrochemical biosensor based on functional composite nanofibers for sensitive
hybridization detection of p53 tumor suppressor using methylene blue (MB) as an
electrochemical indicator is developed. The carboxylated multi-walled carbon
nanotubes (MWNTs) doped nylon 6 (PA6) composite nanofibers (MWNTs–PA6) was
prepared using electrospinning, which served as the nanosized backbone for
pyrrole (Py) electropolymerization. The functional composite nanofibers
(MWNTs–PA6–PPy) used as supporting scaffolds for ssDNA immobilization can
dramatically increase the amount of DNA attachment and the hybridization
sensitivity. The biosensor displayed good sensitivity and specificity. The
target wild type p53 sequence (wtp53) can be detected as low as 50fM and the
discrimination is up to 57.5% between the wtp53 and the mutant type p53 sequence
(mtp53). It holds promise for the early diagnosis of cancer development and
monitoring of patient therapy.
Graphical abstract
Highlights
► A novel
electrochemical p53 biosensor based on functional composite nanofibers
(MWNTs–PA6–PPy) was developed. ► The MWNTs–PA6–PPy electrode with large specific
surface area and good biocompatibility can be used to enhance stability, speed
and sensitivity. ► The biosensor can detect 50fM wild type p53 sequence. ► The
strategy could be extended to develop various sensors for the detection of many
kinds of analytes.
A novel glassy
carbon electrode (GCE) modified with a composite film of poly (4-vinylpyridine)
(P4VP) and multiwalled carbon nanotubes (P4VP/MWCNT GCE) was used for the
voltammetric determination of paracetamol (PCT). This novel electrode displayed
a combined effect of P4VP and MWCNT on the electro-oxidation of PCT in a
solution of phosphate buffer at pH 7. Hence, conducting properties of P4VP along
with the remarkable physical properties of MWCNTs might have combined effects in
enhancing the kinetics of PCT oxidation. The P4VP/MWCNT GCE has also
demonstrated excellent electrochemical activity toward PCT oxidation compared to
that with bare GCE and MWCNT GCE. The anodic peak currents of PCT on the
P4VP/MWCNT GCE were about 300 fold higher than that of the non-modified
electrodes. By applying differential pulse voltammetry technique under optimized
experimental conditions, a good linear ratio of oxidation peak currents and
concentrations of PCT over the range of 0.02–450μM with a limit of detection of
1.69nM were achieved. This novel electrode was stable for more than 60 days and
reproducible responses were obtained at 99% of the initial current of PCT
without any influence of physiologically common interferences such as ascorbic
acid and uric acid. The application of this electrode to determine PCT in
tablets and urine samples was proposed.
Graphical abstract
Highlights
► A P4VP/MWCNT modified
glassy carbon electrode was fabricated and characterized. ► The electrode was
useful for determination of paracetamol. ► At optimum conditions, ascorbic acid
and uric acid did not interfere in the electrode activity. ► The electrode
exhibited good sensitivity, reproducibility and stability. ► The electrode was
used for the determination of paracetamol in formulation tablets and urine
samples.
Isotope dilution
mass spectrometry (IDMS) based on isotope pattern deconvolution (IPD) has been
applied here to MS/MS (QqQ) in order to carry out the quantification and
confirmation of organic compounds in complex matrix water samples without the
use of a methodological IDMS calibration graph. In this alternative approach,
the isotope composition of the spiked sample is measured after fragmentation by
SRM and deconvoluted into its constituting components (molar fractions of
natural abundance and labeled compound) by multiple linear regression (IPD). The
procedure has been evaluated for the determination of the pharmaceutical
diclofenac in effluent and influent urban wastewaters and fortified surface
waters by UHPLC (ESI) MS/MS using diclofenac-d4 as labeled compound.
Calculations were performed acquiring a part and the whole fragment cluster ion,
achieving in all cases recoveries within 90–110% and coefficients of variation
below 5% for all water samples tested. In addition, potential false negatives
arising from the presence of diclofenac-d2 impurities in the labeled compound
were avoided when the proposed approach was used instead of the most usual IDMS
calibration procedure. The number of SRM transitions measured was minimized to
three to make possible the application of this alternative technique in routine
multi-residue analysis.
Graphical abstract
Highlights
► Isotope dilution with
isotope pattern deconvolution (IPD) has been applied to LC–MS/MS. ► The
procedure allows the determination of organic compounds without calibration
graph. ► Diclofenac determination in wastewater showed the need of this
methodology in LC–MS/MS. ► Confirmation was accomplished with routine
transitions used in multiresidue analysis. ► IPD permits the minimal labeling of
the analyte which minimizes isotopic effect.
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