Plasmonic Self‐Propelled Nanomotors for Explosives Detection via Solution‐Based Surface Enhanced Raman Scattering

Abstract

Nanomotors represent a class of artificial machines that span the chasm between molecular motors and bigger micromotors. Their importance lies in the fact that to effectively navigate and perform tasks in a biological environment without alerting the action of the immune system, the maximal size of the object has to be well below 200 nm. Fully nanosized gold/silver core/shell plasmonic nanomotors using the seeded growth wet chemical approach, which allows high scalability of synthesis of the nanomotors compared to planar substrate-based methods, is presented. Using the nanoparticle tracking analysis, the catalysis driven enhanced diffusion of the plasmonic nanomotors in the presence of low concentrations of fuel is presented and shown that the prepared nanomotors are good candidates for a solutionbased surface-enhanced Raman spectroscopy detection of picric acid, a typical explosive. In addition to the mentioned effects, ligand-exchange is performed on the nanomotors to replace the surfactant with its thiolated analog, a combination which is already proven in literature to be stealthy to the immune response of the living organism.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201903041. microjets, [8][9][10][11] Janus particles, [5,12,13] and particle dimers [11] in the past years, showing the possibility to construct micrometer-sized objects with physically and chemically programmed behavior for a specific environment and specific stimuli. [5,14] Such programmed behavior patterns include catalytically driven bubble-jet propulsion, [8] self-electrophoresis, [15][16][17] self-diffusiophoresis, [15,17] selfthermophoresis, [12,17] which are connected to response to external magnetic, [18] electric, [19] or electromagnetic field [20,21] and also to concentration gradients of chemical substances. [22] These micromachines are proposed to be used in biomedicinal [3] and environmental [4,6] as well as in military applications. [23] Applications of micromotors in sensing of small molecules are also developed but in much smaller extent. The sensing is usually based on (i) slowing the micromotors down by catalyst poisoning or accelerating them by providing fuel, [24,25] (ii) aggregation of the micromotors to produce higher concentrations of an analyte [26] or (iii) separation of the sensing of an analyte by collecting the micromotors be sedimentation. [26] However, direct sensing by micromotors is limited.While the area of self-propelled micromachines is well developed, the field of nanorobots, i.e., self-propelled devices of submicrometer size, is developed much less. For any micro-or nanorobots to have real-world impact, we have to use millions and billions of them. Most of the works in the field use planar substrate-based preparation technique. [17] To further push the micro/nanorobots field to real-world applications, one has to develop objects, whose synthesis is easily scalable. [27] The scalability is a property hard to fulfill for the planar-based...

Nanorobots: Machines Squeezed between Molecular Motors and Micromotors

“…21,50,51 Such changes in the synthesis methodology bring the shift from 2D production of the nanorobots to voluminous, scalable synthesis. 52,53…”

“…91 In vivo applied porous silica nanomotors fueled by urease were demonstrated very recently, 32 together with plasmonic nanorobots propelled by hydrogen peroxide decomposition at silver surface with capability of in-situ surface enhanced Raman spectroscopy sensing of explosives. 53…”

“…The colloidal synthesis approach provides a way to address limitations to high-volume nanomotor synthesis. 53 Although environmental remediation is a live topic in the application of catalytic nanomaterials, 98 its connection to self-propelled colloids is still developing. Self-assembly in the colloidal system may shed light on the control of nanomachines.…”

Leukocyte Membrane-Coated Liquid Metal Nanoswimmers for Actively Targeted Delivery and Synergistic Chemophotothermal Therapy

“…In particular, synthetic nanoswimmers may perform diverse operations in the biomedical field, including biosensing [ 13 , 14 ], diagnostics [ 15 , 16 ], precision surgery [ 17 ], laser tissue welding [ 18 ], and direct drug delivery [ 19 , 20 ]. In recent years, various strategies have been employed to propel such micro/nanoswimmers, including chemical reaction [ 21 , 22 ], light stimuli [ 23 – 25 ], and electric [ 26 , 27 ], magnetism [ 28 , 29 ], and acoustic [ 30 , 31 ] actuation. However, most of the nanoswimmers still rely on inorganic materials, such as SiO 2 , mesoporous silicon, and Fe 3 O 4 ; these formulations often fail to be useable in the biosystem for the systemic toxicity or poor biodegradability.…”

Magnetic Nanomotor-Based Maneuverable SERS Probe

“…Our previous work reported a self-propelled "match-like" one-dimensional SERS probe driven by photodecomposition of AgCl, where the phototaxis behavior of the nanomotors was utilized to enrich the SERS probes for an additional enhancement of SERS signal [31]. Novotný et al and Han et al reported SERS probes driven by the decomposition of H 2 O 2 for the detection of explosives and Rhodamine 6G, respectively [59,60]. These motor-based SERS probes performed collective behavior (phototaxis or micromixing) for SERS sensing applications.…”