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Detecting Interactions between Nanomaterials and Cell Membranes by Synthetic Nanopores Binquan Luan,*,† Shuo Zhou,‡ Deqiang Wang,‡ and Ruhong Zhou*,† †
Computational Biology Center, IBM Thomas J. Watson Research, Yorktown Heights, New York 10598, United States Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
‡
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ABSTRACT: Engineered nanomaterials have been increasingly utilized in industry for various consumer products, environmental treatments, energy storage, and biomedical applications. Meanwhile, it has been established that certain nanomaterials can be toxic to biological cells from extensive experimental and theoretical studies. Despite that the exact molecular mechanisms of this nanomaterial toxicity are still not well understood, it is ubiquitous that their interactions with cell membranes, through either endocytosis or penetration (and thus potential lysis), act as the first step toward the inflammation or even the death of a cell. To facilitate the study of nanomaterial−membrane interactions, here we demonstrate a nanopore-based single-molecule approach that can be applied to monitor a specific nanomaterial−membrane interaction in real time. Combined with molecular dynamics and experimental approaches, we show how an ionic current can be used to detect membrane damage by a graphene nanosheet and illustrate the underlying molecular mechanism. More generally, we expect that measured transmembrane ionic currents (both DC and AC) can signify many particle-induced membrane modifications, such as hole formation, particle adsorption, and protein insertion. KEYWORDS: bionano, nanotoxicity, nanopore, biosensor, membrane damage, graphene, nanomaterials actions with biological systems).8,9 Some nanomaterials have been known to induce cytotoxicity to biological cells by damaging cell membranes, similar to protein toxins and amyloid peptides. For example, hydrophobic nanomaterials of particular sizes can penetrate into a cell membrane directly (a passive transport in contrast to endocytosis) and leave open pores in the bilayer.10 A poly(methacrylic acid) (PMAA) coated gold nanoparticle (AuNP) can promote the initial adsorption on a lipid membrane and later abduct a patch of membrane lipids leaving a large hole in the bilayer.11 Additionally, graphene nanosheets have been shown to aggressively extract lipids out of a cell membrane,12,13 causing damage to the membrane. The adsorption of a nanoparticle on a supported lipid bilayer,14 followed by possible damage to the membrane, can be experimentally monitored using atomic force microscopy (AFM)15 or a quartz crystal microbalance with dissipation (QCM-D).11,16 Alternatively, pore formation as a consequence of interactions between nanomaterials and vesicles (with molecular dyes inside) can be discovered by applying fluorescence techniques to optically measure dye leakage.17
T
he membrane of a biological cell encloses cytoplasm, such as cytosol and organelles, and protects the cell from its extracellular environment. Functionally, the membrane regulates the transport of nutrients into and wastes out of a cell. The damage of a cell membrane can often lead to the leakage of intracellular substances (e.g., ions, mRNA, and proteins), which may trigger necrosis for cellular death. During bacterial infection that targets a cell membrane, protein toxins (also known as pore-forming-proteins, such as α-hemolysin from Staphylococcus aureus1) can self-assemble into a transmembrane channel on the host membrane, causing cell lysis or leakage, which is the major mechanism for cellular damage.2 Associated with Alzheimer’s disease (a deadly neurodegeneration disease), amyloid-β 42 peptides (Aβ42), which are intrinsically disordered, can surprisingly aggregate on a cell membrane and form pores with various sizes.3,4 Recently, the same concept or mechanism has been applied to the design of synthesized antibacterial drugs. For example, positively charged peptides or polymers can target the negatively charged bacterial membrane and effectively kill bacteria by forming holes on their membrane.5−7 Engineered nanomaterials have been commercially used in cosmetics, catalysis, microelectronics, food, and drug industries, due to their attractive physical and chemical properties. However, this is accompanied by growing concerns on nanomaterials’ biocompatibility (i.e., potential harmful inter© 2017 American Chemical Society
Received: October 2, 2017 Accepted: November 21, 2017 Published: November 21, 2017 12615
DOI: 10.1021/acsnano.7b07005 ACS Nano 2017, 11, 12615−12623
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Cite This: ACS Nano 2017, 11, 12615−12623
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ACS Nano
membrane and many other engineered nanomaterials, providing a means for evaluating their nanotoxicity in vitro.
To facilitate and simplify experimental detection of nanomaterial−membrane interactions, here, we propose a nanoporebased single-molecule technique that has been widely used to detect biomolecules (such as DNA18 and proteins19) electrochemically. Similar to a black lipid membrane (BLM)14 at macroscale, a patch of lipid bilayer is self-assembled inside a nanometer-sized pore (or generally
