DNA methylation risk score for type 2 diabetes is associated with gestational diabetes.

BACKGROUND: Gestational diabetes mellitus (GDM) and type 2 diabetes mellitus (T2DM) share many pathophysiological factors including genetics, but whether epigenetic marks are shared is unknown. We aimed to test whether a DNA methylation risk score (MRS) for T2DM was associated with GDM across ancestry and GDM criteria. METHODS: In two independent pregnancy cohorts, EPIPREG (n = 480) and EPIDG (n = 32), DNA methylation in peripheral blood leukocytes was measured at a gestational age of 28 ± 2. We constructed an MRS in EPIPREG and EPIDG based on CpG hits from a published epigenome-wide association study (EWAS) of T2DM. RESULTS: With mixed models logistic regression of EPIPREG and EPIDG, MRS for T2DM was associated with GDM: odd ratio (OR)[95% CI]: 1.3 [1.1-1.8], P = 0.002 for the unadjusted model, and 1.4 [1.1-1.7], P = 0.00014 for a model adjusted by age, pre-pregnant BMI, family history of diabetes and smoking status. Also, we found 6 CpGs through a meta-analysis (cg14020176, cg22650271, cg14870271, cg27243685, cg06378491, cg25130381) associated with GDM, and some of their methylation quantitative loci (mQTLs) were related to T2DM and GDM. CONCLUSION: For the first time, we show that DNA methylation marks for T2DM are also associated with GDM, suggesting shared epigenetic mechanisms between GDM and T2DM.

Changes in Oxidative Stress and Intestinal Permeability during Pregnancy in Women with Gestational Diabetes Mellitus Treated with Metformin or Insulin and Healthy Controls: A Randomized Controlled Trial.

Both oxidative stress and intestinal permeability are increased in hyperglycemic situations and have been shown to be reduced by metformin in type 2 diabetes mellitus (T2DM) patients. The aim of this study was to elucidate the effect of metformin on oxidative stress and intestinal permeability in women with gestational diabetes mellitus (GDM) treated with metformin compared to those treated with insulin and healthy controls. A total of 120 women were included from August 2016 to February 2022: 41 received metformin (MET group), 38 received insulin (INS group), and 41 were healthy controls. Baseline and antenatal visits were carried out at 25.4 ± 4.8 and 36.1 ± 0.8 weeks of pregnancy, respectively. Advanced oxidation protein products (AOPPs), total antioxidant capacity (TAC), and zonulin levels were measured at every visit. Zonulin levels from baseline to prepartum visit increased significantly in both healthy controls (0.6 ± 0.9 to 1.2 ± 1.7 ng/mL, p = 0.004) and the INS group (0.4 ± 0.3 to 0.6 ± 0.5 ng/mL, p = 0.034) but did not significantly change in the MET group (0.4 ± 0.4 to 0.5 ± 0.4 ng/mL, p = 0.202). However, TAC and AOPP levels significantly increased in women with GDM, both in the INS and MET groups but not in the healthy controls. In conclusion, in our population, metformin has been shown to avoid an increase in intestinal permeability but failed to avoid an increase in oxidative stress related to hyperglycemia.

Epigenetic Marks as Predictors of Metabolic Response to Bariatric Surgery: Validation from an Epigenome Wide Association Study.

Little is known about the potential role of epigenetic marks as predictors of the resolution of obesity-related comorbidities after bariatric surgery. In this study, 20 patients were classified according to the metabolic improvement observed 6 months after sleeve gastrectomy, based on the diagnosis of metabolic syndrome, into responders if metabolic syndrome reversed after bariatric surgery (n = 10) and non-responders if they had metabolic syndrome bariatric surgery (n = 10). Blood DNA methylation was analyzed at both study points using the Infinium Methylation EPIC Bead Chip array-based platform. Twenty-six CpG sites and their annotated genes, which were previously described to be associated with metabolic status, were evaluated. Cg11445109 and cg19469447 (annotated to Cytochrome P450 2E1 (CYP2E1) gene) were significantly more hypomethylated in the responder group than in the non-responder group at both study points, whilst cg25828445 (annotated to Nucleolar Protein Interacting With The FHA Domain Of MKI67 Pseudogene 3 (NIFKP3) gene) showed to be significantly more hypermethylated in the non-responder group compared to the responder group at both study points. The analysis of the methylation sites annotated to the associated genes showed that CYP2E1 had 40% of the differentially methylated CpG sites, followed by Major Histocompatibility Complex, Class II, DR Beta 1 (HLA-DRB1) (33.33%) and Zinc Finger Protein, FOG Family Member 2 (ZFPM2) (26.83%). Cg11445109, cg19469447 and cg25828445 could have a role in the prediction of metabolic status and potential value as biomarkers of response to bariatric surgery.

Epigenetic marks associated with gestational diabetes mellitus across two time points during pregnancy.

An adverse intrauterine or periconceptional environment, such as hyperglycemia during pregnancy, can affect the DNA methylation pattern both in mothers and their offspring. In this study, we explored the epigenetic profile in maternal peripheral blood samples through pregnancy to find potential epigenetic biomarkers for gestational diabetes mellitus (GDM), as well as candidate genes involved in GDM development. We performed an epigenome-wide association study in maternal peripheral blood samples in 32 pregnant women (16 with GDM and 16 non-GDM) at pregnancy week 24-28 and 36-38. Biochemical, anthropometric, and obstetrical variables were collected from all the participants. The main results were validated in an independent cohort with different ethnic origin (European = 307; South Asians = 165). Two hundred and seventy-two CpGs sites remained significantly different between GDM and non-GDM pregnant women across two time points during pregnancy. The significant CpG sites were related to pathways associated with type I diabetes mellitus, insulin resistance and secretion. Cg01459453 (SELP gene) was the most differentiated in the GDM group versus non-GDM (73.6 vs. 60.9, p = 1.06E-11; FDR = 7.87E-06). Three CpG sites (cg01459453, cg15329406, and cg04095097) were able to discriminate between GDM cases and controls (AUC = 1; p = 1.26E-09). Three differentially methylated positions (DMPs) were replicated in an independent cohort. To conclude, epigenetic marks during pregnancy differed between GDM cases and controls suggesting a role for these genes in GDM development. Three CpGs were able to discriminate GDM and non-GDM groups with high specificity and sensitivity, which may be biomarker candidates for diagnosis or prediction of GDM.

Higher ß cell death in pregnant women, measured by DNA methylation patterns of cell-free DNA, compared to new-onset type 1 and type 2 diabetes subjects: a cross-sectional study.

Diabetes is a metabolic disorder of glucose homeostasis in which ß cell destruction occurs silently and is detected mainly when symptoms appear. In the last few years, it has emerged a great interest in developing markers capable of detecting pancreatic ß cell death focused on improving early diagnosis and getting a better treatment response, mainly in type 1 diabetes. But other types of diabetes would also benefit from early detection of ß cell death. Differentially methylated circulating DNA is being studied as minimally invasive biomarker of cell death. We aimed to explore whether the unmethylated/methylated ratio of the insulin and amylin genes might be a good biomarker of ß cell death in different types of diabetes. A lower index ∆Ct indicates a higher rate of ß-cell death. Plasma samples from subjects without diabetes, pregnant women, pregnant with gestational diabetes (GDM), type 1 diabetes and type 2 diabetes were analyzed. A qPCR reaction with specific primers for both methylated and unmethylated fragments of insulin and amylin genes were carried out. Pregnant women, GDM and non- GDM, showed a higher ß-cell death for both markers (∆INS = 3.8 ± 2.1 and ∆Amylin = 8.5 ± 3.6), whereas T1D presented lower rate (∆INS = 6.2 ± 2.1 and ∆Amylin = 10.7 ± 2.9) comparable to healthy subjects. The insulin methylation index was associated with the newborn birth weight (r = 0.46; p = 0.033) and with insulin resistance (r = -0.533; p = 0.027) in the GDM group. The higher rate of ß-cell death was observed in pregnant women independently of their metabolic status. These indexes could be a good indicator of ß cell death in processes caused by defects on insulin secretion, insulin action, or both.

Criminalización de las protestas sociales en el contexto del covid-19

Durante el proceso de confinamiento por covid-19, se presentaron diversas formas de protesta social que, aunado a la incapacidad de los Gobiernos latinoamericanos de manejar la crisis sanitaria ocasionada por la pandemia, demostraron en la mayoría de los casos que la respuesta del Estado a las movilizaciones y resistencias sociales fue la criminalización de la protesta social, a través de represión y detenciones arbitrarias para tratar de infundir miedo entre la población. Los movimientos generados en el contexto de la pandemia tuvieron diversas y novedosas aristas durante el confinamiento, entre estas el uso de las tecnologías de la información como uno de los elementos clave para la denuncia social y la organización de la protesta para la toma del espacio público. Por otra parte, las demandas de las protestas sociales se centraron principalmente en la insuficiente planeación estratégica de los Gobiernos ante la pandemia, en la precariedad y en el colapso de los sistemas de salud, en el incremento de la violencia de género, del desempleo, de la pobreza, de la desigualdad y de la violencia social.

During the covid-19 confinement process, various forms of social protest were presented, together with the inability of Latin American governments to manage the health crisis caused by the pandemic, demonstrated in most cases that the State's response to social mobilizations and resistance was the criminalization of social protest, through repression and arbitrary detentions to try to instill fear among the population. The movements generated in the context of the pandemic had several and novel edges during the confinement, among them: the use of information technologies as one of the key elements for social denunciation and the organization of protest for the seizure of public space. On the other hand, the demands of the social protests focused mainly on the insufficient strategic planning of governments in the face of the pandemic, on the precariousness and collapse of health systems, on the increase in gender violence, unemployment, poverty, inequality, and social violence.

Epigenome wide association study in peripheral blood of pregnant women identifies potential metabolic pathways related to gestational diabetes.

Gestational diabetes mellitus (GDM) increases the risk of developing metabolic disorders in both pregnant women and their offspring. Factors such as nutrition or the intrauterine environment may play an important role, through epigenetic mechanisms, in the development of GDM. The aim of this work is to identify epigenetic marks involved in the mechanisms or pathways related to gestational diabetes. A total of 32 pregnant women were selected, 16 of them with GDM and 16 non-GDM. DNA methylation pattern was obtained from Illumina Methylation Epic BeadChip, from peripheral blood samples at the diagnostic visit (26-28 weeks). Differential methylated positions (DMPs) were extracted using ChAMP and limma package in R 2.9.10, with a threshold of FDR <0.05, deltabeta >|5|% and B >0. A total of 1.141 DMPs were found, and 714 were annotated in genes. A functional analysis was performed, and we found 23 genes significantly related to carbohydrate metabolism. Finally, a total of 27 DMPs were correlated with biochemical variables such as glucose levels at different points of oral glucose tolerance test, fasting glucose, cholesterol, HOMAIR and HbA1c, at different visits during pregnancy and postpartum. Our results show that there is a differentiated methylation pattern between GDM and non-GDM. Furthermore, the genes annotated to the DMPs could be implicated in the development of GDM as well as in alterations in related metabolic variables.

Behind the Optimization of the Sensor Film: Bioconjugation of Triangular Gold Nanoparticles with Hemoproteins for Sensitivity Enhancement of Enzymatic Biosensors.

Electrochemical biosensors are widely used in a multitude of applications, such as medical, nutrition, research, among other fields. These sensors have been historically used and have not undergone many changes in terms of the involved electrochemical processes. In this work, we propose a new approach on the immobilization and enhancement of the electrochemical properties of the sensing layers through the control and bioconjugation of hemoproteins (hemoglobin, myoglobin, and cytochrome C) on anisotropic gold nanoparticles (gold nanotriangles (AuNTs)). The hemeproteins and the AuNTs are mixed in a solution, resulting in stable bioconjugates that are deposited onto the electrode surface to obtain the biosensors. All the systems proposed herein exhibited direct well-defined redox responses, highlighting the key role of the AuNTs acting as mediators of such electron transfers. Several protein layers surrounding the AuNTs are electroactive, as demonstrated from the charge measured by cyclic voltammetry. The retention of the stability of the hemeproteins once they are part of the bioconjugates is evidenced towards the electrocatalytic reduction of hydrogen peroxide, oxygen, and nitrite. The parameters obtained for the proposed biosensors are similar or even lower than those previously reported for similar systems based on nanomaterials, and they exhibit attractive properties that make them potential candidates for the latest developments in the field of sensing devices.

Insulin Requirement for Gestational Diabetes Control Is Related to Higher Vitamin D Levels up to 1 Year Postpartum: A Prospective Cohort Study.

Vitamin D deficiency is highly prevalent in pregnant women and has been related to a higher risk of gestational diabetes mellitus (GDM). The aim of this study is to analyze vitamin D status evolution in a population of pregnant women with and without GDM. Two-hundred women were included from January 2019 to February 2022 as follows: Control group -CG-, Lifestyle group -LG- (GDM not requiring insulin), and Insulin group -IG- (GDM requiring insulin). Visits were carried out at baseline, antenatal, postpartum, and 1 year after birth. Vitamin D levels, weight, and insulin resistance were measured at every visit. Data about the season, vitamin D supplementation, Mediterranean diet adherence, and physical activity were included. In the three groups, 134 women were included in the CG, 43 in the LG, and 23 in the IG. Vitamin D levels were similar among the groups at baseline, but they were significantly higher in the LG and IG in comparison with the CG at the antenatal visit and significantly higher in the IG vs. CG and LG at the postpartum and 1 year after birth visits. Vitamin D levels were independently related to vitamin D supplementation and the season at baseline, to the season and belonging to the LG or IG at the antenatal visit, and were only independently associated with belonging to the IG at postpartum and 1 year after birth visits. In conclusion, in our population, women with GDM requiring insulin had higher levels of vitamin D in comparison with those not requiring insulin and healthy controls at postpartum and 1 year after pregnancy. Requiring insulin during pregnancy seems to be a factor that independently determines the levels of vitamin D until 1 year after birth. More studies are required to reproduce these data in other populations and to elucidate the mechanisms underlying these findings.

Surface Protection of Quaternary Gold Alloys by Thiol Self-Assembled Monolayers.

This work deals with a physical and chemical surface characterization of quaternary 18K, 14K, and 9K gold alloys and pure polycrystalline gold substrates. Surface microstructure and composition are evaluated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence spectroscopy. Corrosion resistance of 18K gold alloys is explored by potentiodynamic polarization showing the influence of the manufacturing process on materials fabricated as plates and wires. The research is also in the framework of one of the most common strategies on the modification of metallic surface properties, i.e., the building of self-assembled monolayers (SAM) from organic thiols. The metal affinity of the head group to produce the coating of the substrate by covalent binding is approached by using thiol compounds with different molecular structures and functional group chemistries exposed to an electrolyte solution. Therefore, a comparative study on the surface protection of a quaternary 18K gold alloy and pure gold substrates by SAMs of 6-mercaptopurine (6MP), 1-decanethiol (DT), and 11-mercaptoundecanoic acid (MUA) has been carried out. Surface modification and SAM organization are followed by cyclic voltammetry (CV), and the behavior of the double layer of the electrode-electrolyte interface is evaluated by electrochemical impedance spectroscopy (EIS). The study of these materials allows us to extract fundamental knowledge for its potential application in improving the bioactive properties of different jewelry pieces based on 18K gold alloys.

Automatable downstream purification of the benzohydroxamic acid D-DIBOA from a biocatalytic synthesis.

Herbicides play a vital role in agriculture, contributing to increased crop productivity by minimizing weed growth, but their low degradability presents a threat to the environment and human health. Allelochemicals, such as DIBOA (2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4 H)-one), are secondary metabolites released by certain plants that affect the survival or growth of other organisms. Although these metabolites have an attractive potential for use as herbicides, their low natural production is a critical hurdle. Previously, the synthesis of the biologically active analog D-DIBOA (4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one) was achieved, using an engineered E. coli strain as a whole-cell biocatalyst, capable of transforming a precursor compound into D-DIBOA and exporting it into the culture medium, although it cannot be directly applied to crops. Here a chromatographic method to purify D-DIBOA from this cell culture medium without producing organic solvent wastes is described. The purification of D-DIBOA from a filtered culture medium to the pure compound could also be automated. Biological tests with the purified compound on weed models showed that it has virtually the same activity than the chemically synthesized D-DIBOA.

Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures for sensitive and selective SARS-CoV-2 sensing.

The development of DNA-sensing platforms based on new synthetized Methylene Blue functionalized carbon nanodots combined with different shape gold nanostructures (AuNs), as a new pathway to develop a selective and sensitive methodology for SARS-CoV-2 detection is presented. A mixture of gold nanoparticles and gold nanotriangles have been synthetized to modify disposable electrodes that act as an enhanced nanostructured electrochemical surface for DNA probe immobilization. On the other hand, modified carbon nanodots prepared a la carte to contain Methylene Blue (MB-CDs) are used as electrochemical indicators of the hybridization event. These MB-CDs, due to their structure, are able to interact differently with double and single-stranded DNA molecules. Based on this strategy, target sequences of the SARS-CoV-2 virus have been detected in a straightforward way and rapidly with a detection limit of 2.00 aM. Moreover, this platform allows the detection of the SARS-CoV-2 sequence in the presence of other viruses, and also a single nucleotide polymorphism (SNPs). The developed approach has been tested directly on RNA obtained from nasopharyngeal samples from COVID-19 patients, avoiding any amplification process. The results agree well with those obtained by RT-qPCR or reverse transcription quantitative polymerase chain reaction technique.

Amplification-free detection of SARS-CoV-2 using gold nanotriangles functionalized with oligonucleotides.

Gold nanotriangles (AuNTs) functionalized with dithiolated oligonucleotides have been employed to develop an amplification-free electrochemical biosensor for SARS-CoV-2 in patient samples. Gold nanotriangles, prepared through a seed-mediated growth method and exhaustively characterized by different techniques, serve as an improved electrochemical platform and for DNA probe immobilization. Azure A is used as an electrochemical indicator of the hybridization event. The biosensor detects either single stranded DNA or RNA sequences of SARS-CoV-2 of different lengths, with a low detection limit of 22.2 fM. In addition, it allows to detect point mutations in SARS-CoV-2 genome with the aim to detect more infective SARS-CoV-2 variants such as Alpha, Beta, Gamma, Delta, and Omicron. Results obtained with the biosensor in nasopharyngeal swab samples from COVID-19 patients show the possibility to clearly discriminate between non-infected and infected patient samples as well as patient samples with different viral load. Furthermore, the results correlate well with those obtained by the gold standard technique RT-qPCR, with the advantage of avoiding the amplification process and the need of sophisticated equipment.

Electrochemiluminescent nanostructured DNA biosensor for SARS-CoV-2 detection.

This work focuses on the development of an electrochemiluminescent nanostructured DNA biosensor for SARS-CoV-2 detection. Gold nanomaterials (AuNMs), specifically, a mixture of gold nanotriangles (AuNTs) and gold nanoparticles (AuNPs), are used to modified disposable electrodes that serve as an improved nanostructured electrochemiluminescent platform for DNA detection. Carbon nanodots (CDs), prepared by green chemistry, are used as coreactants agents in the [Ru(bpy)3]2+ anodic electrochemiluminescence (ECL) and the hybridization is detected by changes in the ECL signal of [Ru(bpy)3]2+/CDs in combination with AuNMs nanostructures. The biosensor is shown to detect a DNA sequence corresponding to SARS-CoV-2 with a detection limit of 514 aM.

Impact of the Gestational Diabetes Diagnostic Criteria during the Pandemic: An Observational Study.

OBJECTIVE: To analyze the effect of applying alternative diagnostic criteria for gestational diabetes mellitus (GDM) during the COVID-19 pandemic on GDM prevalence and obstetrical and perinatal outcomes, in comparison to usual diagnostic approaches. METHODS: Data from women referred to GDM diagnosis from 1 September to 30 November 2019 were retrospectively collected (2019-group). The same data from the same period in 2020 were prospectively collected (2020-group). In both cases, a two-step diagnostic approach was used, the first step being a screening test (1 h 50 goral glucose tolerance test, OGTT). In 2019 it was followed by a 100 gr OGTT for diagnosis. In 2020, this was replaced by a blood test for the measurement of plasma glucose and HbA1c, according to alternative GDM diagnostic criteria during the COVID-19 pandemic. RESULTS: From 237 women in the 2019 group, 40 (16.9%) were diagnosed with GDM, while from 255 women in the 2020 group, 37 (14.5%) had GDM (p = 0.470). More women in the 2020 group, in comparison to the 2019 group, were nulligravid (41.9% vs. 47.2%, p = 0.013), had a personal history of GDM (11.4% vs. 4.6%, p = 0.013) and had macrosomia in previous pregnancies (10.2% vs. 2.1%, p = 0.001). Obstetrical and perinatal outcomes were similar when comparing women with GDM to non-GDM women in the 2019 and 2020 groups and between GDM women and non-GDM women. CONCLUSION: In a Spanish population, GDM prevalence during the COVID-19 pandemic using the alternative diagnostic criteria was similar to that found in 2019 using the usual diagnostic criteria. Despite women referred for GDM diagnosis during the pandemic having more GDM risk factors, obstetrical and perinatal outcomes were comparable to those observed before the pandemic.

Epigenetic Biomarkers of Transition from Metabolically Healthy Obesity to Metabolically Unhealthy Obesity Phenotype: A Prospective Study.

BACKGROUND: Identifying those parameters that could potentially predict the deterioration of metabolically healthy phenotype is a matter of debate. In this field, epigenetics, in particular DNA methylation deserves special attention. RESULTS: The aim of the present study was to analyze the long-term evolution of methylation patterns in a subset of metabolically healthy subjects in order to search for epigenetic markers that could predict the progression to an unhealthy state. Twenty-six CpG sites were significantly differentially methylated, both at baseline and 11-year follow-up. These sites were related to 19 genes or pseudogenes; a more in-depth analysis of the methylation sites of these genes showed that CYP2E1 had 50% of the collected CpG sites differently methylated between stable metabolically healthy obesity (MHO) and unstable MHO, followed by HLA-DRB1 (33%), ZBTB45 (16%), HOOK3 (14%), PLCZ1 (14%), SLC1A1 (12%), MUC2 (12%), ZFPM2 (12.5%) and HLA-DQB2 (8%). Pathway analysis of the selected 26 CpG sites showed enrichment in pathways linked to th1 and th2 activation, antigen presentation, allograft rejection signals and metabolic processes. Higher methylation levels in the cg20707527 (ZFPM2) could have a protective effect against the progression to unstable MHO (OR: 0.21, 95%CI (0.067-0.667), p < 0.0001), whilst higher methylation levels in cg11445109 (CYP2E1) would increase the progression to MUO; OR: 2.72, 95%CI (1.094-6.796), p < 0.0014; respectively). CONCLUSIONS: DNA methylation status is associated with the stability/worsening of MHO phenotype. Two potential biomarkers of the transition to an unhealthy state were identified and deserve further investigation (cg20707527 and cg11445109). Moreover, the described differences in methylation could alter immune system-related pathways, highlighting these pathways as therapeutic targets to prevent metabolic deterioration in MHO patients.

Distinct thermoresponsive behaviour of oligo- and poly-ethylene glycol protected gold nanoparticles in concentrated salt solutions.

In this work, the methoxy terminated oligo- and polyethylene glycol of different chain lengths (EGn, n = 7, 18, 45 and 136) is grafted on AuNP surfaces under conditions where they attain maximum grafting densities. These EGn-AuNPs gain stability relative to the pristine c-AuNPs in aqueous solutions and in a wide temperature interval and they form stable suspensions in solutions of high NaCl concentrations. To show the thermoresponsive properties of these EGn-AuNPs, temperature titration experiments are carried out in the presence of increasing amounts of salts. The concentrations of NaCl are chosen by checking the stability of EGn-AuNPs at room temperature and choosing the highest concentrations that allow them to form stable suspensions. The analysis of the temperature titration experiments monitored by UV-visible spectroscopy and dynamic light scattering allows us to establish the existence of transitions from individual to assembled nanoparticles, the reversibility of the temperature transitions and hysteretic behaviour in these systems. While EG7-AuNPs only show reversible temperature transitions in the presence of 5 mM NaCl, EG18-AuNPs do up to 1 M NaCl, becoming only partially reversible in 2 M NaCl. The titrations of EG45-AuNPs in 3 and 5 M NaCl show irreversible temperature transitions. Finally, EG136-AuNPs present a complex and interesting behaviour with two temperature transitions, the first one showing hysteresis and the second being reversible.

Effective replacement of cetyltrimethylammonium bromide (CTAB) by mercaptoalkanoic acids on gold nanorod (AuNR) surfaces in aqueous solutions.

The highly packed cetyltrimethylammonium bromide (CTAB) bilayer built up on the surface of gold nanorods (AuNRs) when synthesized by the seed-mediated procedure hampers the complete ligand exchange under experimental conditions that preserves the stability of the dispersions. In the present work, a ligand exchange protocol by using carboxy-terminated alkanethiols of different chain lengths by means of a green approach that uses only aqueous solutions is presented. The protocol is based on the knowledge of the stability in the aqueous solution of both the starting CTAB-AuNRs and the final products that help in the choice of the experimental conditions used for ligand exchange. The characterization of the CTAB protective layer as well as the study of its colloidal stability in solution has helped us to design an appropriate methodology. Cyclic voltammetry of CTAB-AuNRs demonstrates the high stability of the bilayer showing the existence of a two-dimensional phase transition from a highly ordered to a less organized phase. Other techniques such as XPS, FT-IR and Raman spectroscopy provide information about the structure of the layer and UV-visible-NIR spectroscopy establishes the stability conditions in aqueous solution. We have chosen an exchange procedure for 11-mercaptoundecanoic acid (MUA) and 16-mercaptohexadecanoic acid (MHDA) based on a one-pot methodology under conditions where all the species involved are stable. The protocol, however, can be extended to different chemical functionalities that are considered useful to be applied in living systems. Under these conditions the complete exchange of CTAB by the mercaptoderivatives was successful as demonstrated by the different characterization techniques used: UV-visible-NIR, FT-IR, Raman, XPS spectroscopy, cyclic voltammetry and transmission electron microscopy (TEM).

Hemoglobin becomes electroactive upon interaction with surface-protected Au nanoparticles.

In this work, we report on the electrochemical behavior of bioconjugates prepared with gold nanoparticles (AuNP) capped with three different molecular layers (citrate anions, 6-mercaptopurine and ω-mercaptoundecanoic acid) and the protein hemoglobin (Hb). Freshly formed bioconjugates are deposited on a glassy carbon electrode and assayed for electroactivity. A pair of redox peaks with formal potential at -0.37V is obtained, in contrast with the free Hb protein that is inactive on the glassy carbon substrate. The redox response is typical for quasi-reversible processes allowing the determination of the electron transfer rate constant for the three bioconjugates. Additional evidence of the structural integrity of protein upon forming the bioconjugate is obtained by monitoring the electrochemical response of the Hb heme Fe(III)/Fe(II) redox couple as a function of solution pH. Moreover, the Hb forming the protein corona around the AuNPs show good electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. It has been found that only the first layer of Hb surrounding the AuNPs are electroactive, although some part of the second layer also contribute, pointing to the role of the AuNP in the electrochemical response.