Interaction of gold nanoparticles mediated by captopril and S-nitrosocaptopril: the effect of manganese ions in mild acid medium

Surfactant-Free Chitosan/Cellulose Acetate Phthalate Nanoparticles: An Attempt to Solve the Needs of Captopril Administration in Paediatrics

The Paediatric Committee of the European Medicines Agency encourages research into medicinal products for children, in particular, the development of an age-appropriate formulation of captopril is required in the cardiovascular therapeutic area. The aim of this study was the development of a liquid formulation using nanoparticles based only on chitosan and cellulose acetate phthalate containing captopril for the treatment of hypertension, heart failure and diabetic nephropathy in paediatric patients. Nanoparticles were prepared by a nanoprecipitation method/dropping technique without using surfactants, whose use can be associated with toxicity. A range of different cellulose to chitosan weight ratios were tested. A good encapsulation efficiency (61.0 ± 6.5%) was obtained when a high chitosan concentration was used (1:3 ratio); these nanoparticles (named NP-C) were spherical with a mean diameter of 427.1 ± 32.7 nm, 0.17 ± 0.09 PDI and +53.30 ± 0.95 mV zeta potential. NP-C dispersion remained stable for 28 days in terms of size and drug content and no captopril degradation was observed. NP-C dispersion released 70% of captopril after 2 h in pH 7.4 phosphate buffer and NP-C dispersion did not have a cytotoxicity effect on neonatal human fibroblasts except at the highest dose tested after 48 h. As a result, chitosan/cellulose nanoparticles could be considered a suitable platform for captopril delivery in paediatrics for preparing solid/liquid dosage forms.

The effect of pH and transition metal ions on cysteine-assisted gold aggregation for a distinct colorimetric response

Colorimetric detection is a promising sensing strategy that is applicable to qualitative and quantitative determination of an analyte by monitoring visually detectable color changes with the naked eye. This study explored the cysteine (Cys)-induced aggregation of gold nanoparticles (AuNPs) in order to develop a sensitive colorimetric detection method for Cys. For this purpose, we systematically investigated the colorimetric response of AuNPs to Cys with varying particle sizes and concentrations. The AuNPs with various diameters ranging from 26.5 nm to 58.2 nm were synthesized by the citrate reduction method. When dispersed in water to have the same surface area per unit volume, the smaller AuNPs (26.5 nm) exhibited a more sensitive response to Cys compared to a larger counterpart (46.3 nm). We also examined the effect of divalent first-row transition metal ions (Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) on the Cys-induced aggregation of AuNPs. Among the tested metal ions, the addition of Cu²⁺ provided the highest enhancement in sensitivity to Cys regardless of pH between 3.5 and 7. The significant increase in the sensitivity caused by Cu²⁺ could be attributed to the capability of Cu²⁺ to form a highly stable chelate complex with surface-immobilized Cys, facilitating the aggregation of AuNPs. For the AuNPs–Cu²⁺ system at pH 7, the detection limit for Cys was determined to be 5 nM using UV-vis spectroscopy. The reported strategy showed the potential to be used for a rapid and sensitive detection of Cys and also metal ions that can facilitate Cys-mediated aggregation of AuNPs.

Divalent transition metal ions facilitated the aggregation of gold nanoparticles: Fe²⁺ < Ni²⁺ < Zn²⁺ < Co²⁺ ≪ Mn²⁺ < Cu²⁺ at pH 7. The optimized AuNPs-Cu²⁺ system produced the progressive color change upon the addition of cysteine (0.2–2.0 μM).

Nucleophilicity of cysteine and related biothiols and the development of fluorogenic probes and other applications

Biothiols such as l-cysteine, l-homocysteine, and glutathione play essential roles in many biological processes, and are directly associated with several health conditions. Therefore, the development of fast, selective, sensitive, and inexpensive methods for quantitatively analyzing biothiols in aqueous solution, but especially in biological samples, is a very attractive research field. In this feature review, we have approached the relevance of biothiols' nucleophilicity to develop selective fluorogenic probes. Since biothiols have considerable structural similarity, relevant strategies are in full development, including several fluorescent molecular platforms, specific receptor sites, reaction conditions, and optical responses. All of these features are properly presented and discussed. Biothiol sensing protocols are based on traditional organic chemistry reactions such as (hetero)aromatic nucleophilic substitution, addition, and substitution at carbonyl carbon, conjugate addition, and nucleophilic substitution at saturated carbon, amongst others including combined processes; furthermore, mechanistic aspects are detailed herein, including some interesting historical contexts. The feasibility of related fluorogenic probes is illustrated by analysis in complex matrices such as serum, cells, tissues, and animal models. Applications of these reactions in more complex systems such as sulfhydryl-based peptides and proteins are also presented, aiming at functionalizing and detecting these nucleophiles. Most literature cited in this review is recent; however, some other prominent works are also detailed. It is believed that this review may be accessible for many academic levels and may efficiently contribute not only to popularizing science but also to the rational development of fluorogenic probes for biothiol sensing.

Gold Nanoparticles as Colorimetric Sensors for the Detection of DNA Bases and Related Compounds

Results regarding interaction of colloidal gold solutions with nucleobases, including uracil (U), as well as its sulfur derivatives, 2-thiouracil (2TU) and 4-thiouracil (4TU), cytosine (C), adenine (A), and guanine (G), as well as urea and thiourea (TU), are reported. Anionic stabilized citrate gold nanoparticles (AuNPs) were synthesized by reducing the tetrachloroaurate (III) trihydrate with trisodium citrate. The surface plasmon resonance (SPR) band was used in the characterization of synthesized AuNPs, as well as transmission electron microscope (TEM) imaging, which was used in the characterization of dispersed and aggregated gold nanoparticles. Interactions of nucleobases with the gold surface was analyzed by following the plasmon absorbance band red shift of the AuNPs. The sulfur-containing compounds adsorbed to the nanoparticle surfaces by chemisorption-type interactions; with TU and 4TU, the process is accompanied by a sudden change in color; in contrast, 2TU forms stable functionalized gold nanoparticles. Urea and U do not adsorb to nanoparticle surfaces, but the other heterocyclic bases containing nitrogen interact effectively with the gold surface, causing the assembly of nanoparticles, even though the interparticle self-aggregation process was slower than that mediated by either TU or 4TU. The method is efficient in the colorimetric detection of nucleobases and derivatives at concentration levels on the order of 1 µM.

Selective Naked-Eye Detection of SARS-CoV-2 Mediated by N Gene Targeted Antisense Oligonucleotide Capped Plasmonic Nanoparticles

The current outbreak of the pandemic coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) demands its rapid, convenient, and large-scale diagnosis to downregulate its spread within as well as across the communities. But the reliability, reproducibility, and selectivity of majority of such diagnostic tests fail when they are tested either to a viral load at its early representation or to a viral gene mutated during its current spread. In this regard, a selective "naked-eye" detection of SARS-CoV-2 is highly desirable, which can be tested without accessing any advanced instrumental techniques. We herein report the development of a colorimetric assay based on gold nanoparticles (AuNPs), when capped with suitably designed thiol-modified antisense oligonucleotides (ASOs) specific for N-gene (nucleocapsid phosphoprotein) of SARS-CoV-2, could be used for diagnosing positive COVID-19 cases within 10 min from the isolated RNA samples. The thiol-modified ASO-capped AuNPs agglomerate selectively in the presence of its target RNA sequence of SARS-CoV-2 and demonstrate a change in its surface plasmon resonance. Further, the addition of RNaseH cleaves the RNA strand from the RNA-DNA hybrid leading to a visually detectable precipitate from the solution mediated by the additional agglomeration among the AuNPs. The selectivity of the assay has been monitored in the presence of MERS-CoV viral RNA with a limit of detection of 0.18 ng/μL of RNA having SARS-CoV-2 viral load. Thus, the current study reports a selective and visual "naked-eye" detection of COVID-19 causative virus, SARS-CoV-2, without the requirement of any sophisticated instrumental techniques.

How gold nanoparticles can be used to probe the structural changes of a pH-responsive hydrogel

Gold nanoparticles (GNPs) have UV-visible absorption spectra that are highly sensitive to their local environment due to their surface plasmon resonance (SPR). Furthermore, GNPs are able to quench the fluorescence of suitable dyes depending on the GNP-dye separation. Both of these features have led to the use of GNPs as spectroscopic rulers. In this study we sought to use GNPs as spectroscopic probes to investigate the local structural changes associated with the macroscopic pH-triggered swelling/de-swelling transitions of a pH-responsive hydrogel. The hydrogel used in this study comprised covalently inter-linked pH-responsive poly(ethylacrylate-co-methacrylic acid-co-divinyl benzene) microgel particles (MGs). MGs are crosslinked polymer colloids that swell when the pH approaches the pK_a of the constituent polymer. The interlinked MG hydrogels are termed doubly crosslinked microgels (DX MGs) and are a new family of hydrogels. They had polymer volume fractions (ϕ_p) that strongly decreased as the pH increased. UV-visible spectra showed that the wavelength of the SPR absorption (λ_max) for the DX MG/GNP gels was pH-responsive. A linear relationship was found between λ_max and ϕ_p for ϕ_p values up to ∼0.80. The inclusion of Rhodamine 6G within the DX MG/GNP hydrogels resulted in metal-induced fluorescence quenching which was studied using photoluminescence (PL) spectroscopy. The extent of quenching was pH-dependent and was also proportional to ϕ_p. The results of the study showed that the pH-triggered changes of the nanoscale and macroscopic swelling for the DX MGs were similar and imply that affine swelling occurred, which is a new observation. The data suggest that UV-visible or PL spectroscopy could be used to study the swelling of pH-responsive hydrogels containing GNPs remotely.

Aspheric Solute Ions Modulate Gold Nanoparticle Interactions in an Aqueous Solution: An Optimal Way To Reversibly Concentrate Functionalized Nanoparticles

Nanometer-sized gold particles (AuNPs) are of peculiar interest because their behaviors in an aqueous solution are sensitive to changes in environmental factors including the size and shape of the solute ions. In order to determine these important characteristics, we performed all-atom molecular dynamics simulations on the icosahedral Au144 nanoparticles each coated with a homogeneous set of 60 thiolates (4-mercaptobenzoate, pMBA) in eight aqueous solutions having ions of varying sizes and shapes (Na(+), K(+), tetramethylamonium cation TMA(+), tris-ammonium cation TRS(+), Cl(-), and OH(-)). For each solution, we computed the reversible work (potential of mean of force) to bring two nanoparticles together as a function of their separation distance. We found that the behavior of pMBA protected Au144 nanoparticles can be readily modulated by tuning their aqueous environmental factors (pH and solute ion combinations). We examined the atomistic details on how the sizes and shapes of solute ions quantitatively factor in the definitive characteristics of nanoparticle-environment and nanoparticle-nanoparticle interactions. We predict that tuning the concentrations of nonspherical composite ions such as TRS(+) in an aqueous solution of AuNPs be an effective means to modulate the aggregation propensity desired in biomedical and other applications of small charged nanoparticles.

Functional, water-dispersible gold nanoparticles produced with N,N′-bis(acryloyl)-(l)-cystine

Functional CiBA–AuNPs, with optical properties identical to those of TSC–AuNPs, for crosslinking reactions have no need for ligand exchange steps.