Manuel Algarra

Luminescent carbon nanoparticles: effects of chemical functionalization, and evaluation of Ag+ sensing properties

Luminescent carbon-based nanoparticles, addressed as carbon dots (CDs), were synthesized at relatively low temperature from lactose following an easy and inexpensive procedure. Modification of their surface was done by functionalization with mercaptosuccinic acid (MSA) (CDs–MSA). Transmission electron microscopy images showed regular spherical nanoparticles of 5 nm diameter. Raw and functionalized (CDs–MSA) CDs were highly fluorescent at 448 and 472 nm, with relative high quantum yield (Φ = 0.21 and 0.46 respectively). At the maximum fluorescence of CDs–MSA the intensity was quenched by addition of Ag+ ions by a static mechanism with a Stern–Volmer constant of 3.7 × 103 M−1. The analysis of the emission spectra showed that the CD–MSA complex was stable after this process. The quenching profiles showed that only 44% of the CD–MSA fluorophores are accessible to Ag+. The main figures of merit were detection and quantification limits of 385.8 nM and 1.2 μM respectively, and the precision as relative standard deviation was 1.76%. No interference was observed when other metal ions were present indicating a high selectivity for Ag+ detection. The results showed that CDs–MSA can be used for efficient quantification of Ag+ in silver nanoparticle dissolution.

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G(4) dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K(SV)=65(5)×10(4) M(-1); ACNB, K(SV)=19(2)×10(4) M(-1); and, MNP, K(SV)=33(1)×10(2) M(-1). These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L(-1) for MNB and ACNB and about 0.1 mg L(-1) for MNP. No interferences or small interferences are observed for trinitrotoluene [K(SV)=10(2)×10(2)×M(-1)], 2,4-dinitrotoluene [K(SV)=20(3)×10 M(-1)], 2,6-dinitrotoluene [K(SV)=11(4)×10 M(-1)] and nitrobenzene [K(SV)=2(1)×10(3)×M(-1)].

Thiolated DAB dendrimers and CdSe quantum dots nanocomposites for Cd(II) or Pb(II) sensing

Four different generation of thiol-DAB dendrimers were synthesized, S-DAB-G(x) (x=1, 2, 3 and 5), and coupled with CdSe quantum dots, to obtain fluorescent nanocomposites as metal ions sensing. Cd(II) and Pb(II) showed the higher enhancement and quenching effects respectively towards the fluorescence of S-DAB-G(5)-CdSe nanocomposite. The fluorescence enhancement provoked by Cd(II) can be linearized using a Henderson-Hasselbalch type equation and the quenching provoked by Pb(II) can be linearized by a Stern-Volmer equation. The sensor responds to Cd(II) ion in the 0.05-0.7μM concentration range and to Pb(II) ion in the 0.01-0.15mM concentration range with a LOD of 0.06mM. The sensor has selectivity limitations but its dendrimer configuration has analytical advantages.

A novel approach to size separation of gold nanoparticles by capillary electrophoresis–evaporative light scattering detection

A simple and rapid methodology to separate and characterize gold nanoparticles (AuNPs) in aqueous medium by capillary electrophoresis–evaporative light scattering detection (CE–ELSD) is presented. First, a controlled synthesis procedure to obtain water-soluble AuNPs, by varying the trisodium citrate concentration was described. These free AuNPs were separated by capillary zone electrophoresis (CZE) based on the differences in the charge-to-mass ratio of the AuNPs–citrate in a mixed buffer of ammonium acetate (20 mM), containing tris(hydroxymethyl)-aminomethane (Tris, 20 mM) and 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS; 10 mM) at pH 8.5. Under optimal working conditions, three small different-sized AuNPs were successfully separated whose average sizes were 3.5, 6.5 and 10.5 nm. The average diameter was lower than 1.2 nm for all of them (calculated by high-resolution transmission electron microscopy, TEM). Thus, this CE-based method was able to separate AuNPs that differ by only 3 nm in diameter. It can be a valuable methodology for the rapid and cost-effective characterization of other nanomaterials in the future in aqueous solutions.

Current analytical strategies for C-reactive protein quantification in blood.

The measurement of serum C-reactive protein (CRP) levels has been given particular interest as a marker of inflammation associated with cardiovascular diseases. CRP belongs to the pentraxin family of proteins and the routine clinical analysis of CRP in blood samples is used as an important factor in primary prevention programmes together with causative and predisposing factors. This review focuses on the most representative methodologies and strategies for CRP detection and quantification that have been recently proposed, as well as reviewing those that are currently being developed for the specific, sensitive, inexpensive and high-throughput blood analysis of this protein.

Microwave-assisted synthesis of carbon dots and its potential as analysis of four heterocyclic aromatic amines

Fluorescent water soluble carbon nanoparticles, in short carbon dots (CDs), was synthesized from lactose by microwave assisted hydrochloric acid method. Characterized by TEM and DLS to obtain the morphology shape (average 10nm in size), with a higher negative surface charge supported by the composition was obtained by XPS spectroscopy. The maximum of the emission was centered at 450 nm with a lifetime of 2.1 ns. Without further functionalization of the CDs a nanosensor was obtained that responded exponentially to HAAs in the 0.35-0.45 mg L(-1) concentration range by fluorescence static quenching, demonstrated by the lifetime analysis of the CDs in presence of HAAs. Some amino compounds were selected as model for interferences to evaluate the selectivity of this method, showing a notorious added value, with recoveries around 98%. The accuracy of the method was in terms of RSD about 2.5%. The results suggest their promising applications in chemical sensing.

Fluorescent chemosensor for pyridine based on N-doped carbon dots

Fluorescent carbon dots (CDs) and its nitrogen doped (N-CDs) nanoparticles have been synthesized from lactose as precursor using a bottom-up hydrothermal methodology. The synthesized nanoparticles have been characterized by elemental analysis, FTIR, Raman, TEM, DLS, XPS, and steady-state and life-time fluorescence. The synthesized carbon nanoparticles, CDs and N-CDs, have a size at about 7.7±2.4 and 50±15nm, respectively, and quantum yields of 8% (CDs) and 11% (N-CDs). These techniques demonstrated the effectiveness of the synthesis procedure and the functionalization of the CDs surface with amine and amide groups in the presence of NH3 in aqueous media. The effect of excitation wavelength and pH on the luminescent properties was studied. Under the optimal conditions, the nitrogen doped nanoparticles can be used as pyridine sensor in aqueous media because they show an enhancement of its fluorescence with a good linear relationship. The analytical method is simple, reproducible and very sensitive for pyridine determination.

Determination of enantiomeric excess by chiral liquid chromatography without enantiomerically pure starting standards.

A facile approach for the enantiomeric excess determination of enantiomeric mixtures without the necessity of pure enantiomer standards is presented. Promethazine and trimeprazine commercial nonracemic mixtures were used as cases study to probe the validity of the method. Chromatographic resolutions obtained with a chiral column AGP in reverse phase mode were 1.32-1.16 (promethazine) and 1.20-0.93 (trimeprazine) for the three detectors (circular dichroism, photometric and fluorimetric) in series. Results obtained showed that enantiomeric excess was 10.4, 8.71 and 8.58% for promethazine and 1.60, 1.23 and 1.80% for trimeprazine (medium values of 9.23 ± 1.01% and 1.54 ± 0.29%, respectively). Recovery assay over human serum samples, at three concentration levels, spiked with prometazine and submitted to solid-phase extraction, gave values of 99.09-93.48% [S-(-) enantiomer] and 98.51-91.89% [R-(+)-enantiomer]. Detection limits of promethazine enantiomers were between 0.02 µg (fluorimetric) and 1 µg (circular dichroism), and 0.02-1.1 µg for trimeprazine.

Comparison of adipocere formation in four soil types of the Porto (Portugal) district.

Four typical soils of the Porto (Portugal) area were characterized and used to study the decomposition of buried pieces of pork meat under controlled laboratory experiments (an 8 month experiment with a relatively high soil moisture and a 1 month experiment with relatively low soil moisture). The soils types were: organic, sandy, gravel and clay-gravel soils. Soils were characterized for their grain size distribution, pH, water content, organic matter percentage and mineral composition. Four free fatty acids (myristic, palmitic, oleic and stearic) were analysed (using a methodology based on an extraction step followed by a derivatization reaction and high performance liquid chromatography analysis) in soil samples as a sign of adipocere formation. The direct sensorial analysis of the buried sample residues and the free fatty acids profiles of the sampled soils showed that sandy and clay-gravel soils (in a low moisture environment) slowed the normal decomposition process promoting the formation of adipocere. Nevertheless, this apparent soil effect is indirect and a consequence of the different water retention and permeability of the soils. Thus, the water content of the soils is a crucial factor for adipocere formation.

Determination of asulam by fast stopped-flow chemiluminescence inhibition of luminol/peroxidase.

An efficient, sensitive and fast stopped-flow method has been developed to determine asulam in water, based on its inhibition effect on the horseradish peroxidase-luminol-hydrogen peroxide chemiluminescence reaction, (HRP-luminol-H(2)O(2)). Ultra fast data acquisition (0.20s) facilitates excellent selectivity because no interferences from concomitants in the matrix act in such short time scale. The precision as repeatability (expressed as relative standard deviation, n=10) was 0.4% at a 40 pM level. The detection limit was 1.5 pM (0.35 ng/L) and 7.15 pM in pure and raw water, respectively. The calibration data over the range 5-60 pM present a correlation coefficient of r=0.9993. The proposed method has been applied to determine asulam in water samples by using solid-phase extraction (SPE). Mean recovery value was 98.1+/-2% at 50 pM level.