Electrochemical methods for nanotoxicity assessment

Novel Methods and Approaches for Safety Evaluation of Nanoparticle Formulations: A Focus Towards In Vitro Models and Adverse Outcome Pathways

Nanotoxicology is an emerging field employed in the assessment of unintentional hazardous effects produced by nanoparticles (NPs) impacting human health and the environment. The nanotoxicity affects the range between induction of cellular stress and cytotoxicity. The reasons so far reported for these toxicological effects are due to their variable sizes with high surface areas, shape, charge, and physicochemical properties, which upon interaction with the biological components may influence their functioning and result in adverse outcomes (AO). Thus, understanding the risk produced by these materials now is an important safety concern for the development of nanotechnology and nanomedicine. Since the time nanotoxicology has evolved, the methods employed have been majorly relied on in vitro cell-based evaluations, while these simple methods may not predict the complexity involved in preclinical and clinical conditions concerning pharmacokinetics, organ toxicity, and toxicities evidenced through multiple cellular levels. The safety profiles of nanoscale nanomaterials and nanoformulations in the delivery of drugs and therapeutic applications are of considerable concern. In addition, the safety assessment for new nanomedicine formulas lacks regulatory standards. Though the in vivo studies are greatly needed, the end parameters used for risk assessment are not predicting the possible toxic effects produced by various nanoformulations. On the other side, due to increased restrictions on animal usage and demand for the need for high-throughput assays, there is a need for developing and exploring novel methods to evaluate NPs safety concerns. The progress made in molecular biology and the availability of several modern techniques may offer novel and innovative methods to evaluate the toxicological behavior of different NPs by using single cells, cell population, and whole organisms. This review highlights the recent novel methods developed for the evaluation of the safety impacts of NPs and attempts to solve the problems that come with risk assessment. The relevance of investigating adverse outcome pathways (AOPs) in nanotoxicology has been stressed in particular.

A Multidisciplinary Approach Toward High Throughput Label-Free Cytotoxicity Monitoring of Superparamagnetic Iron Oxide Nanoparticles

Abstract: This paper focuses on cytotoxicity examination of superparamagnetic iron oxide nanoparticles (SPIONs) using different methods, including impedance spectroscopy. Recent advances of SPIONs for clinical and research applications have triggered the need to understand their effects in cells. Despite the great advances in adapting various biological and chemical methods to assess in-vitro toxicity of SPIONs, less attention has been paid on the development of a high throughput label-free screening platform to study the interaction between the cells and nanoparticles including SPIONs. In this paper, we have taken the first step toward this goal by proposing a label-free impedimetric method for monitoring living cells treated with SPIONs. We demonstrate the effect of SPIONs on the adhesion, growth, proliferation, and viability of neuroblastoma 2A (N2a) cells using impedance spectroscopy as a label-free method, along with other standard microscopic and cell viability testing methods as control methods. Our results have shown a decreased viability of the cells as the concentration of SPIONs increases with percentages of 59%, 47%, and 40% for 100 µg/mL (C4), 200 µg/mL (C5), 300 µg/mL (C6), respectively. Although all SPIONs concentrations have allowed the growth of cells within 72 hours, C4, C5, and C6 showed slower growth compared to the control (C1). The growth and proliferation of N2a cells are faster in the absence or low concentration of SPIONS. The percent coefficient of variation (% CV) was used to compare cell concentrations obtained by TBDE assay and a Scepter cell counter. Results also showed that the lower the SPIONs concentration, the lower the impedance is expected to be in the sensing electrodes without the cells. Meanwhile, the variation of surface area (∆S) was affected by the concentration of SPIONs. It was observed that the double layer capacitance was almost constant because of the higher attachment of cells, the lower surface area coated by SPIONs. In conclusion, impedance changes of electrodes exposed to the mixture of cells and SPIONs offer a wide dynamic range (>1 MΩ using Electric Cell-substrate Impedance electrodes) suitable for cytotoxicity studies. Based on impedance based, viability testing and microscopic methods' results, SPIONs concentrations higher than 100 ug/mL and 300 ug/mL cause minor and major effects, respectively. We propose that a high throughput impedance-based label-free platform provides great advantages for studying SPIONs in a cell-based context, opening a window of opportunity to design and test the next generation of SPIONs with reduced toxicity for biomedical or medical applications.

Differential lethal and sublethal effects in embryonic zebrafish exposed to different sizes of silver nanoparticles

Various parameters can influence the toxic response to silver nanoparticles (Ag NPs), including the size and surface properties, as well as the exposure environment and the biological site of action. Herein, we assess the intestinal toxicity of three different sizes (10, 40, and 100 nm) of Ag NPs in embryonic zebrafish, and describe the relationship between the properties and behavior of Ag NPs in the exposure medium, and induction of lethal and sublethal effects. We find that the composition of the medium and the size contribute to differential NPs agglomeration, release of Ag ions, and subsequent effects during exposure. The exposure medium causes dramatic reduction in silver dissolution due to the presence of salts and divalent cations, which limits the lethal potential of silver ions. Lethality is observed primarily for embryos exposed to medium sized Ag NPs (40 nm), but not to the supernatant originated from particles, which suggests that the exposure to particulate silver is the main cause of mortality. On the other hand, the exposure to 10 nm and 100 nm NPs, as well as Ag ions, only causes sublethal developmental defects in skeletal muscles and intestine, and induces a nitric oxide imbalance.

Is "nano safe to eat or not"? A review of the state-of-the art in soft engineered nanoparticle (sENP) formulation and delivery in foods

With superior physicochemical properties, soft engineered nanoparticles (sENP) (protein, carbohydrate, lipids and other biomaterials) are widely used in foods. The preparation, functionalities, applications, transformations in gastrointestinal (GI) tract, and effects on gut microbiota of sENP directly incorporated for ingestion are reviewed herein. At the time of this review, there is no notable report of safety concerns of these nanomaterials found in the literature. Meanwhile, various beneficial effects have been demonstrated for the application of sENP. To address public perception and safety concerns of nanoscale materials in food, methodologies for evaluation of physiological effects of nanomaterials are reviewed. The combination of these complementary methods will be useful for the establishment of a comprehensive risk assessment system.

Linking nanomaterial properties to biological outcomes: analytical chemistry challenges in nanotoxicology for the next decade

This article provides our perspective on the analytical challenges in nanotoxicology as the field is entering its third decade.

Modern Approaches to Chemical Toxicity Screening

Chemical toxicity has a serious impact on public health, and toxicity failures of drug candidates drive up drug development costs. Many in vitro bioassays exist for toxicity screening, and newer versions of these tend to be high throughput or high content assays, some of which rely on electrochemical detection. Toxicity very often results from metabolites of the chemicals we are exposed to, so it is important that assays feature metabolic conversion. Combining bioassays, computational predictions, and accurate chemical pathway elucidation presents our best chance for reliable toxicity prediction. Employing electrochemical and electrochemiluminescent approaches, cell-free microfluidic arrays can measure relative rates of formation of DNA-metabolite adduct formation (a measure of genotoxicity) as well as DNA oxidation levels resulting from enzyme-generated metabolites. Enzymes for several organ types can be studied simultaneously. These arrays can be used to identify the most reactive metabolites, and subsequent mechanistic details can then be investigated with high throughput LC-HPLC using enzyme/DNA-coated magnetic beads.

Bioapplications of Electrochemical Sensors and Biosensors

Recent progress in the electrochemical field enabled development of miniaturized sensing devices that can be used in biological settings to obtain fundamental and practical biochemically relevant information on physiology, metabolism, and disease states in living systems. Electrochemical sensors and biosensors have demonstrated potential for rapid, real-time measurements of biologically relevant molecules. This chapter provides an overview of the most recent advances in the development of miniaturized sensors for biological investigations in living systems, with focus on the detection of neurotransmitters and oxidative stress markers. The design of electrochemical (bio)sensors, including their detection mechanism and functionality in biological systems, is described as well as their advantages and limitations. Application of these sensors to studies in live cells, embryonic development, and rodent models is discussed.

Quantum Dot Nanotoxicity Investigations Using Human Lung Cells and TOXOR Electrochemical Enzyme Assay Methodology

Recent studies have suggested that certain nanomaterials can interfere with optically based cytotoxicity assays resulting in underestimations of nanomaterial toxicity. As a result there has been growing interest in the use of whole cell electrochemical biosensors for nanotoxicity applications. Herein we report application of an electrochemical cytotoxicity assay developed in house (TOXOR) in the evaluation of toxic effects of mercaptosuccinic acid capped cadmium telluride quantum dots (MSA capped CdTe QDs), toward mammalian cells. MSA capped CdTe QDs were synthesized, characterized, and their cytotoxicity toward A549 human lung epithelial cells investigated. The internalization of QDs within cells was scrutinized via confocal microscopy. The cytotoxicity assay is based on the measurement of changes in cellular enzyme acid phosphatase upon 24 h exposure to QDs. Acid phosphatase catalyzes dephosphorylation of 2-naphthyl phosphate to 2-naphthol (determined by chronocoulometry) and is indicative of metabolic activity in cells. The 24 h IC50 (concentration resulting in 50% reduction in acid phosphatase activity) value for MSA capped CdTe QDs was found to be 118 ± 49 μg/mL using the TOXOR assay and was in agreement with the MTT assay (157 ± 31 μg/mL). Potential uses of this electrochemical assay include the screening of nanomaterials, environmental toxins, in addition to applications in the pharmaceutical, food, and health sectors.

C. elegans-on-a-chip for in situ and in vivo Ag nanoparticles' uptake and toxicity assay

Nanomaterials are extensively used in consumer products and medical applications, but little is known about their environmental and biological toxicities. Moreover, the toxicity analysis requires sophisticated instruments and labor-intensive experiments. Here we report a microfluidic chip incorporated with the nematode Caenorhabditis elegans that rapidly displays the changes in body growth and gene expression specifically responsive to the silver nanoparticles (AgNPs). C. elegans were cultured in microfluidic chambers in the presence or absence of AgNPs and were consequently transferred to wedge-shaped channels, which immobilized the animals, allowing the evaluation of parameters such as length, moving distance, and fluorescence from the reporter gene. The AgNPs reduced the length of C. elegans body, which was easily identified in the channel of chip. In addition, the decrease of body width enabled the worm to advance the longer distance compared to the animal without nanoparticles in a wedge-shaped channel. The transgenic marker DNA, mtl-2::gfp was highly expressed upon the uptake of AgNPs, resulting in green fluorescence emission. The comparative investigation using gold nanoparticles and heavy-metal ions indicated that these parameters are specific to AgNPs. These results demonstrate that C. elegans-on-a-chip has a great potential as a rapid and specific nanoparticle detection or nanotoxicity assessment system.

Biomolecular detection at ssDNA-conjugated nanoparticles by nano-impact electrochemistry

We describe the use of ssDNA functionalized silver nanoparticle (AgNP) probes for quantitative investigation of biorecognition and real time detection of biomolecular targets using nano-impact electrochemistry. The method is based on measurements of the individual collision events between ssDNA aptamer-functionalized AgNPs and a carbon fiber miroelectrode (CFME). Specific binding events of target analyte induced collision frequency changes enabling ultrasensitive detection of the aptamer target in a single step. These changes are assigned to the surface coverage of the NP by the ssDNA aptamers and subsequent conformational changes of the aptamer probe which affect the electron transfer between the NP and the electrode surface. The method enables sensitive and selective detection of ochratoxin A (OTA), chosen here as a model target, with a limit of detection of 0.05nM and a relative standard deviation of 4.9%. The study provides a means of characterizing bioconjugation of AgNPs with aptamers and assessing biomolecular recognition events with high sensitivity and without the use of exogenous reagents or enzyme amplification steps. This methodology can be broadly applicable to other bioconjugated systems, biosensing and related bioanalytical applications.

Electrochemical monitoring of colloidal silver nanowires in aqueous samples

Silver nanowires (NWs) are increasingly utilized in technological materials and consumer products, but an effective analytical technique is not yet available to measure their concentration in the environment. Here, we present an electrochemical method to quantify Ag NWs suspended in aqueous solution. Using linear sweep voltammetry, the Ag NWs are identified by the peak potential while their concentration is revealed by the intensity of the peak current. The peak current varies linearly with the Ag NW concentration with a low detection limit of 3.50 ng mL(-1). This method is also successfully applied to quantify Ag NWs in mixtures with nanoparticles, through their specific oxidation behavior, and in wastewater obtained after the Ag NW film preparation process.