Comparative contributions of copper nanoparticles and ions to copper bioaccumulation and toxicity in barnacle larvae

Copper-Nanoparticle-Induced Neurotoxic Effect and Oxidative Stress in the Early Developmental Stage of Zebrafish (Danio rerio)

Copper nanoparticles (CuNPs) are extensively used in electronics, cosmetics, fungicides, and various other fields due to their distinctive qualities. However, this widespread usage can contribute to environmental contamination and heightened health risks for living organisms. Despite their prevalent use, the ecological impacts and biosafety of CuNPs remain inadequately understood. The present study aims to delve into the potential toxic effects of CuNPs on zebrafish (Danio rerio) embryos, focusing on multiple indexes such as embryonic development, neurotoxicity, oxidative stress, and inflammatory response. The results revealed a notable increase in the death rate and deformity rate, alongside varying degrees of decrease in hatching rate and heart rate following CuNPs exposure. Particularly, the frequency of spontaneous tail coiling significantly declined under exposure to CuNPs at concentrations of 500 µg/L. Furthermore, CuNPs exposure induced alterations in the transcriptional expression of GABA signaling pathway-related genes (gabra1, gad, abat, and gat1), indicating potential impacts on GABA synthesis, release, catabolism, recovery, and receptor binding. Additionally, CuNPs triggered oxidative stress, evidenced by disruption in superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, along with elevated malondialdehyde (MDA) levels. This oxidative stress subsequently led to a proinflammatory cascade, as demonstrated by the increased transcriptional expression of inflammatory markers (il-1β, tnf-α, il-6, and il-8). Comparative analysis with copper ion (provided as CuCl2) exposure highlighted more significant changes in most indexes with CuCl2, indicating greater toxicity compared to CuNPs at equivalent concentrations. In conclusion, these findings provide valuable insights into the toxic effects of CuNPs on zebrafish embryo development and neurotransmitter conduction. Furthermore, they present technical methodologies for assessing environmental and health risks associated with CuNPs, contributing to a better understanding of their biosafety and ecological impact.

An overview on dispersion procedures and testing methods for the ecotoxicity testing of nanomaterials in the marine environment

Considerable efforts have been devoted to develop or adapt existing guidelines and protocols, to obtain robust and reproducible results from (eco)toxicological assays on engineered nanomaterials (NMs). However, while many studies investigated adverse effects of NMs on freshwater species, less attention was posed to the marine environment, a major sink for these contaminants. This review discusses the procedures used to assess the ecotoxicity of NMs in the marine environment, focusing on the use of protocols and methods for preparing NMs dispersions and on the NMs physicochemical characterization in exposure media. To this purpose, a critical analysis of the literature since 2010 was carried out, based on the publication of the first NMs dispersion protocols. Among the 89 selected studies, only <5 % followed a standardized dispersion protocol combined with NMs characterization in ecotoxicological media, while more than half used a non-standardized dispersion method but performed NMs characterization. In the remaining studies, only partial or no information on dispersion procedures or on physicochemical characterization was provided. This literature review also highlighted that metal oxides NMs were the most studied (42 %), but with an increasing interest in last years towards nanoplastics (14 %) and multicomponent nanomaterials (MCNMs, 7 %), in line with the growing attention on these emerging contaminants. For all these NMs, primary producers as algae and bacteria were the most studied groups of marine species, in addition to mollusca, while organisms at higher trophic levels were less represented, likely due to challenges in evaluating adverse effects on more complex organisms. Thus, despite the wide use of NMs in different applications, standard dispersion protocols are not often used for ecotoxicity testing with marine species. However, the efforts to characterize NMs in ecotoxicological media recognize the importance of following conditions that are as standardized as possible to support the ecological hazard assessment of NMs.

Copper nanoparticles and silver nanoparticles impair lymphangiogenesis in zebrafish

Lymphatic system distributes in almost all vertebrate tissues and organs, and plays important roles in the regulation of body fluid balance, lipid absorption and immune monitoring. Although CuNPs or AgNPs accumulation has been reported to be closely associated with delayed hatching and motor dysfunction in zebrafish embryos, their biological effects on lymphangiogenesis remain unknown. In this study, thoracic duct was observed to be partially absent in both CuNPs and AgNPs stressed zebrafish larvae. Specifically, CuNPs stress induced hypermethylation of E2F7/8 binding sites on CCBE1 promoters via their producing ROS, thereby leading to the reduction of binding enrichment of E2F7/8 on CCBE1 promoter and its subsequently reduced expression, then resulting in defective lymphatic vessel formation. Differently, AgNPs stress induced down-regulated CCBE1 expression via down-regulating mRNA and protein levels of E2F7/8 transcription factors, thereby resulting in defective lymphatic vessel formation. This study may be the first to demonstrate that CuNPs and AgNPs damaged lymphangiogenesis during zebrafish embryogenesis, mechanistically, CuNPs epigenetically regulated the expression of lymphangiogenesis regulator CCBE1 via hypermethylating its promoter binding sites of E2F7/8, while AgNPs via regulating E2F7/8 expression. Meanwhile, overexpression of ccbe1 mRNA effectively rescued the lymphangiogenesis defects in both AgNPs and CuNPs stressed larvae, while overexpression of e2f7/8 mRNA effectively rescued the lymphangiogenesis defects in AgNPs rather than CuNPs stressed larvae. The results in this study will shed some light on the safety assessment of nanomaterials applied in medicine and on the ecological security assessments of nanomaterials. Video Abstract.

Behavior and toxicity assessment of copper nanoparticles in aquatic environment: A case study on red swamp crayfish

With the wide use of copper nanoparticles (CuNPs) in various industrial and commercial applications, they inevitably enter the aquatic environment. However, their behavior in the aquatic environment and potential toxicity to aquatic organisms remain little known. In this study, we investigated the behavior of CuNPs in freshwater, as well as the toxicity and bioaccumulation of CuNPs and copper sulfate (CuSO₄), used as a positive control for copper ions toxicity, in red swamp crayfish (Procambarus clarkii). The results showed that CuNPs released copper ions into freshwater and aggregated rapidly in freshwater, and their release of copper ions and aggregation slowed down at a higher concentration of CuNPs. The calculated 72-h LC₅₀ values for crayfish were 1.18 and 0.54 mg/L for CuNPs and CuSO₄, respectively. Cu accumulation in the gill and hepatopancreas from CuSO₄ treatments was significantly higher than that from CuNPs, and the highest Cu bioaccumulation level in crayfish was found in the gill, followed by hepatopancreas and muscle with the exposure of copper. The activities of the antioxidative enzymes in the crayfish significantly decreased after exposure to CuNPs for 48 h, compared to the control (without CuNPs or CuSO₄). Histological examination revealed that there was no significant alteration of hepatopancreas in the crayfish exposed to CuNPs. Meanwhile, the growth of crayfish was not significantly inhibited by CuNPs. These results suggested that CuNPs exposure can induce oxidative stress in the crayfish, gill is the main tissue for their accumulation, and their toxicity is mainly caused by the released copper ions.

Environmental Fate of Metal Nanoparticles in Estuarine Environments

In the last decade, metal engineered nanomaterials (ENMs) have seen an exponential use in many critical technologies and products, as well an increasing release into the environment. Coastal ecosystems worldwide may receive ENM-polluted waters and wastes, with a consequent alteration of habitats and contamination of aquatic biota. There is a scarcity of data regarding the fate of these emerging contaminants in such environments. Open issues include the determination of the sources, the quantification of the interactions with marine sediments, the bioaccumulation pathways, the ecotoxicology on marine fauna and the identification of the principal biotic and abiotic factors that may alter metal ENMs toxicity. Little is known about their potential transference into the food web, as well toxicity features and co-stressors of single or multiple ENMs under laboratory and real environmental conditions for various taxonomic phyla. This review reports current knowledge on the ecological impact of ENMs under the complex environmental conditions of estuary systems, identifies gaps in current knowledge and provides directions for future research.

Toxic Effects of Copper Nanoparticles on Paramecium bursaria–Chlorella Symbiotic System

Although many reports have demonstrated that nanoparticles can have a negative effect on aquatic organisms, the toxic effects on symbiotic organisms remain poorly understood. The present study conducts ultrastructure, enzyme activity, and transcriptomics to assess the toxic effects to the Paramecium bursaria–Chlorella symbiotic system from exposure to copper nanoparticles (CuNPs) for 24 h. We found that in both the host and symbiotic algae, CuNP exposure induced high reactive oxygen species level, which leads to oxidative damage and energy metabolism disorder. Moreover, transmission electron micrographs (TEMs) showed that the symbiotic algae in the cytoplasm of P. bursaria were enveloped in the digestive vacuole and digested, and the level of acid phosphatase activity increased significantly within 24 h, which indicated that the stability of the symbiotic system was affected after CuNP exposure. We speculated that the increased energy demand in the host and symbiotic algae resulted from oxidative stress, precipitating the decrease of the photosynthetic products provided to the host, the digestion of the symbiont, and the destruction of the stable symbiotic relationship. The study provides the first insight into the mechanisms of nanoparticles’ toxicity to the symbiotic relationship in the ecosystem, which may help to understand the environmental effects and toxicological mechanisms of nanoparticles.

Effect of Copper Nanoparticles and Ions on Epididymis and Spermatozoa Viability of Chinese Soft-Shelled Turtles Pelodiscus sinensis

Copper nanoparticles (CuNPs) have been widely used in various industrial and commercial applications, which become a potential threat to aquatic organisms. Nevertheless, their potential toxicity to the epididymis and sperm remains little known. In this study, we evaluated the effect of CuNPs and copper ions (CuSO4) on the spermatozoa viability, epididymal structure, antioxidant enzyme activity, and inflammatory cytokines in cauda epididymis of the Chinese soft-shelled turtle. Results showed that the spermatozoa viability of Chinese soft-shelled turtles decreased significantly with an increase in CuNPs or Cu ions concentrations. The epithelial cells of the epididymal duct of the Chinese soft-shelled turtles with the treatment of 5 mg kg−1 CuNPs were slightly swollen, and the connective tissue between the epididymal ducts was loose. The epithelial structure of the epididymal tube was severely damaged with an increase in Cu ion concentrations. Compared to the control, the antioxidative enzymes activities and the expression of IL-1β, TNF-α, and IL-6 mRNA in the epididymis significantly increased with the treatment of CuNPs or CuSO4. The present study revealed that Cu ions exert more harmful effect on the epididymis and spermatozoa viability of Chinese soft-shelled turtles than copper nanoparticles.

Emerging investigator series: metal nanoparticles in freshwater: transformation, bioavailability and effects on invertebrates

MNPs may undergo different environmental transformations in aquatic systems, consequently changing their mobility, bioavailability and toxicity to freshwater invertebrates.

Biocide effect against SARS-CoV-2 and ESKAPE pathogens of a noncytotoxic silver-copper nanofilm

Nanometric materials with biocidal properties effective against severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and pathogenic bacteria could be used to modify surfaces, reducing the risk of touching transmission. In this work, we showed that a nanometric layer of bimetallic AgCu can be effectively deposited on polypropylene (PP) fibers. The virucidal properties of the AgCu nanofilm were evaluated by comparing the viral loads remaining on uncoated and coated PP after contact times between 2 and 24 h. Quantification of virion numbers for different initial concentrations indicated a reduction of more than 95% after 2 h of contact. The bactericidal action of the AgCu nanofilm was also confirmed by inoculating uncoated and coated PP with a pool of pathogenic bacteria associated with pneumonia (ESKAPE). Meanwhile, no cytotoxicity was observed for human fibroblasts and keratinocyte cells, indicating that the nanofilm could be in contact with human skin without threat. The deposition of the AgCu nanofilm on the nonwoven component of reusable cloth masks might help to prevent virus and bacterial infection while reducing the pollution burden related to the disposable masks. The possible mechanism of biocide contact action was studied by quantum chemistry calculations that show that the addition of Ag and/or Cu makes the polymeric fiber a better electron acceptor. This can promote the oxidation of the phospholipids present at both the virus and bacterial membranes. The rupture at the membrane exposes and damages the genetic material of the virus. More studies are needed to determine the mechanism of action, but the results reported here indicate that Cu and Ag ions are good allies, which can help protect us from the virus that has caused this disturbing pandemic.

Microplastic ingestion induces asymmetry and oxidative stress in larvae of the sea urchin Pseudechinus huttoni

Determining the effects of microplastic (MP) ingestion by marine organisms, especially during the sensitive larval stages, is an important step in understanding wider ecosystem responses. We investigated the ingestion, retention (1-5 μm), and short-term exposure effects (1-4 μm) of spherical MPs by larvae of the sea urchin Pseudechinus huttoni. Larvae ingested MPs in a dose-dependent manner and successfully egested particles after a short retention period. Survival was not significantly affected by exposure to MPs over the 10-day experimental period, however, a teratogenic response in terms of delayed development resulted in an increase of larval arm asymmetry. Additionally, MP exposure resulted in oxidative damage to lipids and proteins in larval body tissue despite a significant upregulation of antioxidant defences. The findings indicate MP exposure may impair cellular function, leading to negative consequences for an organism's fitness and survival.

The effects of engineered nanoparticles on nitrification during biological wastewater treatment

Technological advancements in the past few decades have made it possible to manufacture nanomaterials at a large scale, and engineered nanoparticles (ENPs) are increasingly found in consumer products, such as cosmetics, sports products, and LED displays. A large amount of these ENPs end up in wastewater and potentially impact the performance of wastewater treatment plants (WWTPs). One important function of the WWTP is nitrification, which is carried out by the actions of two groups of bacteria, ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB). Since most ENPs are found to have or are designed to have antimicrobial activities, it is a legitimate concern that ENPs entering WWTPs may have negative impacts on nitrification. In this paper, the effects of ENPs on nitrification are discussed, focusing mainly on autotrophic nitrification by AOBs and NOBs. This review also covers ENP effects on anaerobic ammonium oxidation (anammox). Generally, nitrifiers in pure and mixed cultures can be inhibited by a variety of ENPs, but stress response mechanisms may attenuate toxicity. Long-term studies demonstrated that a wide range of NPs could cause severe deterioration of AOBs and/or NOBs when the influent concentration exceeded an inhibition threshold. Proposed mechanisms include the generation of reactive oxygen species, dissolved metals, physical disruption of cell membranes, bacterial engulfment, and intracellular accumulation of ENPs. Future research needs are also discussed.

Metal- and metal/oxide-based engineered nanoparticles and nanostructures: a review on the applications, nanotoxicological effects, and risk control strategies

The production and demand of nanoparticles in the manufacturing sector and personal care products, release a large number of engineered nanoparticles (ENPs) into the atmosphere, aquatic ecosystems, and terrestrial environments. The intentional or involuntary incorporation of ENPs into the environment is carried out through different processes. The ENPs are combined with other compounds and release into the atmosphere, settling on the ground due to the water cycle or other atmospheric phenomena. In the case of aquatic ecosystems, the ENPs undergo hetero-aggregation and sedimentation, reaching different living organisms and flora, as well as groundwater. Accordingly, the high mobility of ENPs in diverse ecosystems is strongly related to physical, chemical, and biological processes. Recent studies have been focused on the toxicological effects of a wide variety of ENPs using different validated biological models. This literature review emphasizes the study of toxicological effects related to using the most common ENPs, specifically metal and metal/oxides-based nanoparticles, addressing different synthesis methodologies, applications, and toxicological evaluations. The results suggest negative impacts on biological models, such as oxidative stress, metabolic and locomotive toxicity, DNA replication dysfunction, and bioaccumulation. Finally, it was consulted the protocols for the control of risks, following the assessment and management process, as well as the classification system for technological alternatives and risk management measures of ENPs, which are useful for the transfer of technology and nanoparticles commercialization.

"Nanosize effect" in the metal-handling strategy of the bivalve Scrobicularia plana exposed to CuO nanoparticles and copper ions in whole-sediment toxicity tests

To date, the occurrence, fate and toxicity of metal-based NPs in the environment is under investigated. Their unique physicochemical, biological and optical properties, responsible for their advantageous application, make them intrinsically different from their bulk counterpart, raising the issue of their potential toxic specificity or "nanosize effect". The aim of this study was to investigate copper bioaccumulation, subcellular distribution and toxic effect in the marine benthic species Scrobicularia plana exposed to two forms of sediment-associated copper, as nanoparticles (CuO NPs) and as soluble ions (CuCl₂). Results showed that the exposure to different copper forms activated specific organism's metal handling strategies. Clams bioaccumulated soluble copper at higher concentrations than those exposed to sediment spiked with CuO NPs. Moreover, CuO NPs exposure elicited a stronger detoxification response mediated by a prompt mobilization of CuO NPs to metal-containing granules as well as a delayed induction of MT-like proteins, which conversely, sequestered soluble copper since the beginning of the exposure at levels significantly different from the control. Eventually, exposure to high concentrations of either copper form led to the same acute toxic effect (100% mortality) but the outcome was delayed in bivalves exposed to CuO NPs suggesting that the mechanisms underlying toxicity were copper form-specific. Indeed, while most of soluble copper was associated to the mitochondrial fraction suggesting an impairment of the ATP synthesis capacity at mitochondrial level, CuO NPs toxicity was most likely caused by the oxidative stress mediated by their bioaccumulation in the enzymatic and mitochondrial metabolically available fractions.

Copper Surfaces in Biofilm Control

Biofilms are structures comprising microorganisms associated to surfaces and enclosed by an extracellular polymeric matrix produced by the colonizer cells. These structures protect microorganisms from adverse environmental conditions. Biofilms are typically associated with several negative impacts for health and industries and no effective strategy for their complete control/eradication has been identified so far. The antimicrobial properties of copper are well recognized among the scientific community, which increased their interest for the use of these materials in different applications. In this review the use of different copper materials (copper, copper alloys, nanoparticles and copper-based coatings) in medical settings, industrial equipment and plumbing systems will be discussed considering their potential to prevent and control biofilm formation. Particular attention is given to the mode of action of copper materials. The putative impact of copper materials in the health and/or products quality is reviewed taking into account their main use and the possible effects on the spread of antimicrobial resistance.

Engineered metal nanoparticles in the marine environment: A review of the effects on marine fauna

There is an increasing awareness of how damaging pollutants in the marine environment can be, however information on the effects of metal engineered nanoparticles (ENPs) on marine biota is still insufficient, despite an exponential rising in related publications in recent years. In order to provide an integrated insight on the present state of the art on metal ENP-related ecotoxicology studies on marine fauna, this review aimed to: (i) highlight the means of toxicity of metal ENPs in the marine environment, (ii) identify the principal biotic and abiotic factors that may alter metal ENP toxicity, and (iii) analyse and categorize results of these studies, including accumulation, molecular and histological biomarkers, genotoxicity and behavioural changes. Data retrieved from Scopus yielded 134 studies that met pre-established criteria. Most often, the target ENPs were titanium, zinc, copper or silver, and most studies (61.2%) focused on the phylum Mollusca. The degree of toxicity of metal ENPs was often dependent on the concentrations tested, length of exposure and the type of tissue sampled. Effects from simple tissue accumulation to DNA damage or behavioural alterations were identified, even when concentrations below environmentally available levels were used. It is proposed that other phyla besides the traditional Mollusca (and within it Bivalvia) should be used more often in this kind of studies, that exact pathways of toxicity be further explored, and lastly that co-stressors be used in order to best mimic conditions observed in nature. In this review, the current knowledge on engineered metal nanoparticles and their effects on marine fauna was summarized, highlighting present knowledge gaps. Guidelines for future studies focusing on under-developed subjects in ENP toxicology are also briefly provided.

Influence of NOM on the Stability of Zinc Oxide Nanoparticles in Ecotoxicity Tests

Nanomaterials are known to aggregate in the presence of ions. Similarly, the aggregation of zinc oxide nanoparticles (ZnO NPs) exposed to various ions such as sodium chloride and calcium chloride in water systems increases with the ionic strength. Therefore, for accurate toxicity studies, it is necessary to conduct a test using natural organic matters (NOMs) as additional dispersants that strengthen stability with increased repulsive forces. The three types of ecotoxicity tests based on the dispersion stability test using NOM showed that the toxicities of the three test samples decreased in the presence of NOM. To determine how NOM improved dispersion and reduced toxicities, we analyzed the ionization degree of ZnO NPs with and without NOM and found that the solubility was below 2 mg/L with a negligible change over time, implying that the ionization effect was low. The absolute value of the surface charge of particles increased in the presence of NOM, resulting in increased repulsive electrostatic forces and steric hindrance, causing less aggregation and more dispersion. Additionally, although the NOM used in the test is considered an effective dispersant that does not have a toxicological effect on aquatic organisms, the presence of NOM resulted in reduced toxicities and should be further investigated to establish it as a standard test method.

Comparative effects of Cu (60-80 nm) and CuO (40 nm) nanoparticles in Artemia salina: Accumulation, elimination and oxidative stress

In this study, nanotoxicity tests were made by exposure of Artemia salina to copper (Cu 60-80 nm) and copper oxide (CuO 40 nm) nanoparticles (NPs) at different concentrations (0.2, 1, 5, 10, 25, and 50 mg/l) during some exposure duration. Characterization of Cu and CuO NPs were performed using Transmission Electron Microscope (TEM), Dynamic Light Scattering (DLS), Zeta Potential, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transformation Infrared (FT-IR) analyzes. In organisms, the accumulation and elimination rates of NPs was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis and the oxidative stress effects on A. salina were determined by Glutathione (GSH) and Thiobarbituric acid reactive substances (TBARS) analysis methods. Both NPs were found to differ in accumulation and elimination rates at each application time and in parallel with the increase in concentration. In each group, it was determined that ion release increased with application time. The results showed that the accumulation rates in Cu NPs had a tendency to increase at 48 h and to decrease at 72 h in concentrations of 0, 2 and 1 mg/l, respectively. And in the all other concentrations have been seen an increasing trend within the time. In the CuO NPs (40 nm), accumulation rates were a decrease trend at 48th hour and an increase trend at 72nd hour except 10 mg/l concentration. In the 10 mg/l group was an increase trend with the application period. Cu NP, TBARS value increased with increasing concentrations and the highest increase was observed at 24 h of 5 ppm group. The groups showed a tendency to increase-decrease-increase-decrease in TBARS levels in terms of elapsed time (24th, 48th, 72nd hour and elimination) (5 ppm and 10 ppm groups tended to decrease in TBARS level at 72nd hour). TBARS increased with increasing concentration ratios in CuO NPs (40 nm).

Iron-Doping of Copper Oxide Nanoparticles Lowers Their Toxic Potential on C6 Glioma Cells

Copper oxide nanoparticles (CuO-NPs) are well known for their cytotoxicity which in part has been attributed to the release of copper ions from CuO-NPs. As iron-doping has been reported to reduce the susceptibility of CuO-NPs to dissolution, we have compared pure CuO-NPs and CuO-NPs that had been doped with 10% iron (CuO-Fe-NPs) for copper release and for their toxic potential on C6 glioma cells. Physicochemical characterization revealed that dimercaptosuccinate (DMSA)-coated CuO-NPs and CuO-Fe-NPs did not differ in their size or zeta potential. However, the redox activity and liberation of copper ions from CuO-Fe-NPs was substantially slower compared to that from CuO-NPs, as demonstrated by cyclic voltammetry and by the photometric quantification of the copper ion-bathocuproine complex, respectively. Exposure of C6 cells to these NPs caused an almost identical cellular copper accumulation and each of the two types of NPs induced ROS production and cell toxicity. However, the time- and concentration-dependent loss in cell viability was more severe for cells that had been treated with CuO-NPs compared to cells exposed to CuO-Fe-NPs. Copper accumulation and toxicity after exposure to either CuO-NPs or CuO-Fe-NPs was prevented in the presence of copper chelators, while neutralization of the lysosomal pH by bafilomycin A1 prevented toxicity without affecting cellular copper accumulation or ROS production. These data demonstrate that iron-doping does not affect cellular accumulation of CuO-NPs and suggests that the intracellular liberation of copper ions from CuO-NPs is slowed by the iron doping, which in turn lowers the cell toxic potential of iron-doped CuO-NPs.

Copper oxide nanoparticles as an effective anti-biofilm agent against a copper tolerant marine bacterium, Staphylococcus lentus

Biofilm formation on antifouling coatings is a serious concern in seawater cooling systems and the maritime industry. A prolific biofilm forming strain (Staphylococcus lentus), possessing high tolerance (>1,000 µg ml^-1) to dissolved copper ions (Cu⁺⁺) was isolated from titanium coupons exposed in the coastal waters of Kalpakkam, east coast of India. S. lentus formed increased biofilm (p < 0.05) at 100 µg ml^-1 of Cu⁺⁺ ions, when compared with the untreated control. To combat biofilm formation of this strain, the efficacy of copper oxide nanoparticles synthesized from copper nitrate by varying the concentrations of hexamine and cetyl trimethyl ammonium bromide (CTAB), was investigated. Complete (100%) inhibition of biofilm formation was observed with plain CuO NP (0.5 M hexamine, uncapped) at 1,000 µg ml^-1. Capping with CTAB, influenced the morphology and the purity of the synthesized CuO NPs but did not alter their surface charge. Capping reduced metal ion release from CuO NPs and their antibacterial and anti-biofilm property against S. lentus. Overall, uncapped CuO NPs were effective in controlling biofilm formation of S. lentus. Concurrent release of copper ions and contact mediated physical damage by CuO NPs offer a promising approach to tackle metal tolerant biofilm bacteria.