In Situ Quantification of Silver Nanoparticle Dissolution Kinetics in Simulated Sweat Using Linear Sweep Stripping Voltammetry

Silver nanoparticle interactions with glycated and non-glycated human serum albumin mediate toxicity

Introduction: Biomolecules bind to and transform nanoparticles, mediating their fate in biological systems. Despite over a decade of research into the protein corona, the role of protein modifications in mediating their interaction with nanomaterials remains poorly understood. In this study, we evaluated how glycation of the most abundant blood protein, human serum albumin (HSA), influences the formation of the protein corona on 40 nm silver nanoparticles (AgNPs) and the toxicity of AgNPs to the HepG2 human liver cell line. Methods: The effects of glycation on AgNP-HSA interactions were quantified using circular dichroism spectroscopy to monitor protein structural changes, dynamic light scattering to assess AgNP colloidal stability, zeta potential measurements to measure AgNP surface charge, and UV-vis spectroscopy and capillary electrophoresis (CE) to evaluate protein binding affinity and kinetics. The effect of the protein corona and HSA glycation on the toxicity of AgNPs to HepG2 cells was measured using the WST cell viability assay and AgNP dissolution was measured using linear sweep stripping voltammetry. Results and Discussion: Results from UV-vis and CE analyses suggest that glycation of HSA had little impact on the formation of the AgNP protein corona with protein-AgNP association constants of ≈2x10⁷ M^-1 for both HSA and glycated HSA (gHSA). The formation of the protein corona itself (regardless of whether it was formed from HSA or glycated HSA) caused an approximate 2-fold decrease in cell viability compared to the no protein AgNP control. While the toxicity of AgNPs to cells is often attributed to dissolved Ag(I), dissolution studies showed that the protein coated AgNPs underwent less dissolution than the no protein control, suggesting that the protein corona facilitated a nanoparticle-specific mechanism of toxicity. Overall, this study highlights the importance of protein coronas in mediating AgNP interactions with HepG2 cells and the need for future work to discern how protein coronas and protein modifications (like glycation) may alter AgNP reactivity to cellular organisms.

Aggregation Kinetics of TiO2 Nanoparticles in Human and Artificial Sweat Solutions: Effects of Particle Properties and Sweat Constituents

Dermal penetration potentials of titanium dioxide nanoparticles (TiO₂ NPs) may be affected by aggregation upon contact with sweat. This study investigated the aggregation kinetics of three TiO₂ NPs in thirty human sweat samples and four artificial sweat standards. Effects of particle concentration, sweat type, and inorganic (sodium chloride, disodium hydrogen phosphate, and sodium dihydrogen phosphate) and organic (l-histidine, lactic acid, and urea) constituents were examined. Three TiO₂ NPs remained colloidally stable in >20/30 human sweat samples and showed significant negative correlations (P < 0.01) between aggregation rates and |zeta potentials|. They aggregated rapidly over 20 min to >750 nm in three artificial sweat standards, while remained more stable in the International-Standard-Organization-pH-5.5 standard. Aggregation behaviors of three TiO₂ NPs mostly followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, allowing for determining their critical coagulation concentrations in inorganic constituents (15-491 mM) and Hamaker constants (3.3-7.9 × 10^-21 J). Higher concentrations of particles, inorganic constituents, and l-histidine destabilized three TiO₂ NPs, whereas urea inhibited aggregation. Three TiO₂ NPs adsorbed organic sweat constituents via complexation with amino or carboxyl groups, with isotherms following the Langmuir model. Correlation analyses further suggested that the adsorbed organic constituents may stabilize three TiO₂ NPs against aggregation in sweat by steric hindrance.

Dissolved organic matters-enhanced Pb releases from nano- or submicron Pb sulfides and oxides

Diverse lead (Pb) particles possess different ecological risks not only due to their own toxicity differences but also because of different abilities to release toxic dissolved Pb. Dissolved organic matter (DOM) was a key factor influencing dissolution processes of metal particles. However, impacts of DOM on dissolution of different Pb nano- or submicron particles were not known yet. Herein, impacts of DOM on dissolution kinetics of lead sulfide (PbS), lead sulfate (PbSO₄), lead monoxide (PbO), lead tetroxide (Pb₃O₄) and lead dioxide (PbO₂) nano- or submicron particles were firstly investigated taking Pahokee Peat humic acid (PPHA) as an example. Results indicated PPHA improved the suspending stability of Pb particles through electrostatic repulsion, and enhanced releases of dissolved Pb. Final concentration of dissolved Pb was raised by 1.22-8.82 times with PPHA. This was attributed to ligand exchange interactions between PPHA and Pb particles. Theoretical computations indicated that not only sorption or ligand exchange energy, but also numbers of ligands on the surface of particles were key factors governing impacts of PPHA on dissolved Pb. This study provided a new mechanism insight into dissolution behavior of various Pb particles and will be beneficial to their ecological risk assessment.

Effect of polar/non-polar facets on the transformation of nanoscale ZnO in simulated sweat and potential impacts on the antibacterial activity

The use of nanoscale zinc oxide (n-ZnO) in the personal care products would cause interactions between n-ZnO and human sweat. Facet engineering has been applied to n-ZnO to improve its activity. Nevertheless, it is not clear whether the exposed facet would affect transformation of n-ZnO in sweat. Herein, we prepared ZnO nanoneedles with the dominant (1010) non-polar facet (i.e., ZnO-1010) and ZnO nanoflakes with the dominant (0001) polar facet (i.e., ZnO-0001), respectively. We found that n-ZnO can undergo chemical transformation in the simulated sweat within 168 h or 24 h, transforming into amorphous materials and Zn₃(PO₄)₂0.4 H₂O and/or Na(ZnPO₄)·H₂O. Given the rate constant (e.g., 0.093 h^-1 for ZnO-0001 vs. 0.033 h^-1 for ZnO-1010) of ZnO depletion and components of the precipitate from the simulated sweat, nevertheless, the transformation is highly dependent on the dominant exposed facet of n-ZnO. The ZnO-0001 relative to ZnO-1010 would likely undergo chemical transformation, demonstrating that the (0001) polar facet compared to (1010) non-polar facet had a superior activity to the dihydrogen phosphate anions in the simulated sweat, which is supported by density functional theory calculations. The chemical transformation can affect the antibacterial activity of n-ZnO to E. coli, moderating the toxicity due to a great decrease in the concentration of the dissolved zinc. In total, our findings provided insights into the facet-dependent transformation for n-ZnO in the simulated sweat, improving our understanding of potential risk of n-ZnO.

Integrated approaches to testing and assessment for grouping nanomaterials following dermal exposure

Exposure to different nanoforms (NFs) via the dermal route is expected in occupational and consumer settings and thus it is important to assess their dermal toxicity and the contribution of dermal exposure to systemic bioavailability. We have formulated four grouping hypotheses for dermal toxicity endpoints which allow NFs to be grouped to streamline and facilitate risk assessment. The grouping hypotheses are developed based on insight into how physicochemical properties of NFs (i.e. composition, dissolution kinetics, size, and flexibility) influence their fate and hazard following dermal exposure. Each hypothesis is accompanied by a tailored Integrated Approach to Testing and Assessment (IATA) that is structured as a decision tree and tiered testing strategies (TTS) for each relevant question (at decision nodes) that indicate what information is needed to guide the user to accept or reject the grouping hypothesis. To develop these hypotheses and IATAs, we gathered and analyzed existing information on skin irritation, skin sensitization, and dermal penetration of NFs from the published literature and performed experimental work to generate data on NF dissolution in sweat simulant fluids. We investigated the dissolution of zinc oxide and silicon dioxide NFs in different artificial sweat fluids, demonstrating the importance of using physiologically relevant conditions for dermal exposure. All existing and generated data informed the formulation of the grouping hypotheses, the IATAs, and the design of the TTS. It is expected that the presented IATAs will accelerate the NF risk assessment for dermal toxicity via the application of read-across.

Single-Particle Electrochemical Imaging Provides Insights into Silver Nanoparticle Dissolution at the Solution-Solid Interface

Dissolution of nanoparticles is an environmental interfacial process that affects the transformation of nanoparticles. Understanding the dissolution processes of nanoparticles is important to predict their fate in the aquatic environment. However, studying nanoparticle dissolution kinetics is still challenging since dissolution is usually coupled with nanoparticle aggregation. Here, we probed the dissolution process of Ag nanoparticles at the single-particle level by surface plasmon resonance microscopy. The single-particle imaging capability enabled us to classify Ag nanoparticles, measure the dissolution dynamics of single nanoparticles, and correlate the aggregation size with oxidation activity. Moreover, we studied the dual effect of natural organic matter on the dissolution of Ag nanoparticles and validated this result with real natural freshwater. Our study provides new insights into the dissolution of Ag nanoparticles, and this technique can be extended for other nanomaterials to evaluate their fate in aquatic environments.

Monitoring the Cd2+ release from Cd-containing quantum dots in simulated body fluids by size exclusion chromatography coupled with ICP-MS

Quantification of Cd²⁺ release from Cd-containing quantum dots (QDs) is of fundamental importance to elucidate its toxicity to organisms, but remains a great challenge due to the lack of appropriate analytical method. Herein, a facile method based on size exclusion chromatography (SEC) combined with inductively coupled plasma mass spectrometry (ICP-MS) was developed for separating and quantifying the QDs and counterpart ions. By using the mixture of sodium dodecyl sulfate (SDS) and ethylenediaminetetraacetic acid tetrasodium salt (EDTA) as the mobile phase, the defect of QD and ion adsorption onto the SEC column was overcome, thus realizing the accurate quantification of ionic species. Besides, the concentration of QDs was achieved through subtracting the ion concentration from the total concentration. Selecting CdSe@ZnS as the typical QDs, the Cd²⁺ release process in four typical simulated body fluids, namely, simulated gastric fluid, simulated sweat, Gamble's solution, and artificial lysosomal fluid, was monitored using the developed SEC-ICP-MS method. The media pH is identified as the decisive factor which controls the dissolution of ZnS shells and also the Cd²⁺ release kinetics and final concentration. Our results suggest that the oral pathway for QD uptake poses the biggest risk to human health.

Determination of Drugs in Clinical Trials: Current Status and Outlook

All pharmaceutical drugs, vaccines, cosmetic products, and many medical breakthroughs must first be approved through clinical research and trials before advancing to standard practice or entering the marketplace. Clinical trials are sets of tests that are required to determine the safety and efficacy of pharmaceutical compounds, drugs, and treatments. There is one pre-phase and four main clinical phase requirements that every drug must pass to obtain final approval. Analytical techniques play a unique role in clinical trials for measuring the concentrations of pharmaceutical compounds in biological matrices and monitoring the conditions of patients (or volunteers) during various clinical phases. This review focuses on recent analytical methods that are employed to determine the concentrations of drugs and medications in biological matrices, including whole blood, plasma, urine, and breast milk. Four primary analytical techniques (extraction, spectroscopy, chromatography, and electrochemical) are discussed, and their advantages and limitations are assessed. Subsequent to a survey of evidence and results, it is clear that microelectromechanical system (MEMS) based electrochemical sensor and biosensor technologies exhibit several notable advantages over other analytical methods, and their future prospects are discussed.

Chemical transformations of nanoscale zinc oxide in simulated sweat and its impact on the antibacterial efficacy

Nanoscale zinc oxide (n-ZnO) is widely used in personal care products and textiles, thus, it would likely be released into human sweat. To better evaluate the potential human health risks of n-ZnO, it is essential to understand its chemical transformations in physiological solutions, such as human sweat, and the resulting changes in the n-ZnO bioavailability. Here, two types of n-ZnO, ZnO nanoparticles (ZnO-NPs) and nanorod-based ZnO nanospheres (ZnO-NSs) were synthesized and incubated in 3 types of simulated sweat with different pH values and phosphate concentrations. The content of Zn₃(PO₄)₂ in the transformed n-ZnO was quantified by selective dissolution of Zn₃(PO₄)₂ in 0.35 M ammonia solution where 100% and 5.5% of Zn₃(PO₄)₂ and ZnO were dissolved, respectively. The kinetics analysis indicated that by 24-48 h the content of Zn₃(PO₄)₂ reached the maximum, being 15-21% at pH 8.0 and 45-70% at pH 5.5 or 4.3. Interestingly, no correlation was observed between the rate constants of Zn₃(PO₄)₂ formation and the specific surface areas of n-ZnO, implying that chemical transformations from n-ZnO to Zn₃(PO₄)₂ in the simulated sweat might not be simply attributed to dissolution and precipitation. Using a variety of characterization techniques, we demonstrated the formation of a ZnO‒Zn₃(PO₄)₂ core-shell structure with the shell consisting of amorphous Zn₃(PO₄)₂ at pH 8.0 and additionally of crystalline Zn₃(PO₄)₂ and Zn₃(PO₄)₂•4H₂O at pH 5.5 or 4.3. The phosphate-induced transformation of n-ZnO in the simulated sweat at pH 5.5 and 4.3 greatly reduced the antibacterial efficacy of n-ZnO through moderating the nanoparticle dissolution, indicating limited bioavailability of the NPs upon transformation. The results improve the understanding of the fate and hazards of n-ZnO.

A voltammetric investigation of the sulfidation of silver nanoparticles by zinc sulfide

Silver nanoparticles (Ag NPs) are among the most common forms of nanoparticles in consumer products, yet the environmental implications of their widespread use remain unclear due to uncertainties about their fate. Because sulfidation of Ag NPs results in the formation of a stable silver sulfide (Ag₂S) product, it is likely an important removal mechanism of bioavailable silver in natural waters. In addition to sulfide, the complete conversion of Ag NPs to Ag₂S will require dissolved oxygen or some other oxidant so dispersed metal sulfides may be an important pool of reactive sulfide for such reactions in oxygenated systems. The reaction of Ag NPs with zinc sulfide (ZnS) was investigated using a voltammetric method, anodic stripping voltammetry (ASV). ASV provided sensitive, in situ measurements of the release of zinc (Zn²⁺) cations resulting from the cation exchange reaction between Ag NPs and ZnS. The effects of Ag NP size and surface coatings on the initial rates of sulfidation by ZnS were examined. Sulfidation of smaller Ag NPs generally occurred faster and to a greater extent due to their larger relative surface areas. Sulfidation of Ag NPs capped by citrate and lipoic acid occurred more rapidly relative to polyvinylpyrrolidone (PVP) and branched polyethylene (BPEI). This study demonstrates the utility of voltammetry for such investigations and provides insights into important factors controlling Ag NP sulfidation such as availability of dissolved oxygen, Ag NP size and Ag NP surface coating. Furthermore, this work demonstrates the importance of cation exchange reactions between silver and metal sulfides, and how the environmental release of Ag NPs could alter the speciation of other metals of environmental significance.

Effective killing of bacteria under blue-light irradiation promoted by green synthesized silver nanoparticles loaded on reduced graphene oxide sheets

Graphene oxide (GO) materials loaded with silver nanoparticles (AgNPs) have drawn considerable attention due to their capacity to efficiently inactivate bacteria though a multifaceted mechanism of action, as well as for presenting a synergetic effect against bacteria when compared to the activity of AgNPs and GO alone. In this investigation, we present an inexpensive and environmentally-friendly method for synthesizing reduced GO sheets coated with silver nanoparticles (AgNPs/r-GO) using a coffee extract solution as a green reducing agent. The physical and chemical properties of the produced materials were extensively characterized by scanning electron microscopy (SEM), field-emission gun transmission electron microscopy (FEG-TEM), ultraviolet and visible absorption (UV-Vis), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and ion release determination. The results demonstrated that AgNPs/r-GO composites were successfully produced, revealing the formation of micrometer-sized r-GO sheets decorated by AgNPs of approximately 70 nm diameter. Finally, bactericidal and photobactericidal effects of the AgNPs/r-GO composites were tested against Staphylococcus aureus, in which the results showed that the composites presented antimicrobial and photoantimicrobial activities. Moreover, our results demonstrated for the first time, to our knowledge, that an efficient process of bacterial inactivation can be achieved by using AgNPs/r-GO composites under blue light irradiation as a result of three different bacterial killing processes: (i) chemical effect promoted by Ag⁺ ion release from AgNPs; (ii) photocatalytic activity induced by AgNPs/r-GO composites, enhancing the bacterial photoinactivation due to the excited-Plasmons of the AgNPs when anchored on r-GO; and (iii) photodynamic effect produced by bacterial endogenous photosensitizers under blue-light irradiation. In summary, the present findings demonstrated that AgNPs/r-GO can be obtained by a non-toxic procedure with great potential for biomedical-related applications.

Bovine Serum Albumin Enhances Silver Nanoparticle Dissolution Kinetics in a Size- and Concentration-Dependent Manner

The dissolution of silver nanoparticles (AgNPs) to release Ag(I)(aq) is an important mechanism in potentiating AgNP cytotoxicity and imparting their antibacterial properties. However, AgNPs can undergo other simultaneous biophysicochemical transformations, such as protein adsorption, which can mediate AgNP dissolution behaviors. We report the comprehensive analysis of AgNP dissolution and protein adsorption behaviors with monolayer surface coverage of AgNPs by bovine serum albumin (BSA). AgNP dissolution rate constants, k_dissolution, were quantified over several particle sizes (10, 20, and 40 nm) and BSA concentrations (0-2 nM) using linear sweep stripping voltammetry. Across all particle sizes, the dissolution rate constant increased with increasing BSA concentrations. However, protein-enhanced dissolution behaviors were most pronounced for 10 nm AgNPs, which exhibited 3.6-fold and 7.7-fold relative enhancement when compared to 20 and 40 nm AgNPs, respectively. Changes to AgNP surface properties upon interaction with BSA were monitored using dynamic light scattering and zeta potential measurements, while BSA-AgNP complex formation was evaluated using UV-vis spectroscopy and circular dichroism spectroscopy. A subtle increase in the BSA-AgNP association constant was observed with an increase in the AgNP size. Together, these results suggest that the AgNP size dependence of BSA-enhanced dissolution of AgNPs is possibly mediated through both displacement of Ag(I)(aq)-loaded BSA by excess protein in the bulk solution and minimized accessibility of the AgNP surface because of BSA adsorption.