Photoactive Au@MoS2 Micromotors for Dynamic Surface-Enhanced Raman Spectroscopy Sensing.

Photophoretic Au@MoS2 micromotors are used as smart mobile substrates for dynamic surface-enhanced Raman spectroscopy (SERS) sensing. The photophoretic capabilities and swarming-like propulsion of the micromotors allow for their schooling and accumulation in the measuring spot, increasing the density of SERS-active gold nanoparticles for Raman mapping and, simultaneously, the preconcentration of the target analyte. The generation of "hot-microflake spots" directly in the Raman irradiation point results in a 15-18-fold enhancement in the detection of crystal violet without the requirement for additional external sources for propulsion. Moreover, the reproducible collective micromotor motion does not depend on the exact position of the laser spot concerning individual micromotors, which greatly simplifies the experimental setup, avoiding the requirements of sophisticated equipment. The strategy was further applied for the detection of malachite green and paraquat with a good signal enhancement. The new on-the-move-based SERS strategy holds great promise for on-site detection with portable instrumentation in a myriad of environmental monitoring and clinical applications.

The rise of metal-organic framework based micromotors.

Micromotors (MMs) are micro and nanoscale devices capable of converting energy into autonomous motion. Metal-organic frameworks (MOFs) are crystalline materials that display exceptional properties such as high porosity, internal surface areas, and high biocompatibility. As such, MOFs have been used as active materials or building blocks for MMs. In this highlight, we describe the evolution of MOF-based MMs, focusing on the last 3 years. First, we covered the main propulsion mechanisms and designs, from catalytic to fuel-free MOF-based MMs. Secondly, we discuss recent applications of new fuel-free MOFs MM to give a critical overview of the current challenges of this blooming research field. The advantages and challenges discussed provide a useful guide for the design of the next generation MOF MMs toward real-world applications.

Photoresponsive MoS2 and WS2 microflakes as mobile biocide agents.

A fuel-free strategy for the eradication of Escherichia coli and Staphylococcus aureus biofilms using WS2 and MoS2 photophoretic microflakes is described. The microflakes were prepared by liquid-phase exfoliation of the materials. Under electromagnetic irradiation at 480 or 535 nm, the microflakes experience a fast collective behavior at speeds of over 300 µm s-1 due to photophoresis. Simultaneously to their motion, reactive oxygen species are generated. The fast microflake schooling into multiple moving swarms results in a highly efficient "collision" platform that disrupts the biofilm, enhancing radical oxygen species' contact with the bacteria for their inactivation. As such, removal biofilm mass rates of over 90% and 65% are achieved using the MoS2 and WS2 microflakes in the treatment of Gram-negative E. coli and Gram-positive S. aureus biofilms after 20 min. Much lower removal biofilm mass rates (30%) are obtained under static conditions, revealing the crucial role of microflake movement and radical generation in the active eradication of biofilms. Much higher removal efficiencies are observed in biofilm deactivation as compared with the use of free antibiotics, which are not able to destroy the densely packed biofilms. The new moving microflakes hold considerable promise for the treatment of antibiotic-resistant bacteria.

Recent Advances in One-Dimensional Micro/Nanomotors: Fabrication, Propulsion and Application.

Due to their tiny size, autonomous motion and functionalize modifications, micro/nanomotors have shown great potential for environmental remediation, biomedicine and micro/nano-engineering. One-dimensional (1D) micro/nanomotors combine the characteristics of anisotropy and large aspect ratio of 1D materials with the advantages of functionalization and autonomous motion of micro/nanomotors for revolutionary applications. In this review, we discuss current research progress on 1D micro/nanomotors, including the fabrication methods, driving mechanisms, and recent advances in environmental remediation and biomedical applications, as well as discuss current challenges and possible solutions. With continuous attention and innovation, the advancement of 1D micro/nanomotors will pave the way for the continued development of the micro/nanomotor field.

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review.

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Biocompatible micromotors for biosensing.

Micro/nanomotors are nanoscale devices that have been explored in various fields, such as drug delivery, environmental remediation, or biosensing and diagnosis. The use of micro/nanomotors has grown considerably over the past few years, partially because of the advantages that they offer in the development of new conceptual avenues in biosensing. This is due to their propulsion and intermixing in solution compared with their respective static forms, which enables motion-based detection methods and/or decreases bioassay time. This review focuses on the impacts of micro/nanomotors on biosensing research in the last 2 years. An overview of designs for bioreceptor attachment to micro/nanomotors is given. Recent developments have focused on chemically propelled micromotors using external fuels, commonly hydrogen peroxide. However, the associated fuel toxicity and inconvenience of use in relevant biological samples such as blood have prompted researchers to explore new micro/nanomotor biosensing approaches based on biocompatible propulsion sources such as magnetic or ultrasound fields. The main advances in biocompatible propulsion sources for micro/nanomotors as novel biosensing platforms are discussed and grouped by their propulsion-driven forces. The relevant analytical applications are discussed and representatively illustrated. Moreover, envisioning future biosensing applications, the principal advantages of micro/nanomotor synthesis using biocompatible and biodegradable materials are given. The review concludes with a realistic drawing on the present and future perspectives.

MoSBOTs: Magnetically Driven Biotemplated MoS2 -Based Microrobots for Biomedical Applications.

2D layered molybdenum disulfide (MoS2 ) nanomaterials are a promising platform for biomedical applications, particularly due to its high biocompatibility characteristics, mechanical and electrical properties, and flexible functionalization. Additionally, the bandgap of MoS2 can be engineered to absorb light over a wide range of wavelengths, which can then be transformed into local heat for applications in photothermal tissue ablation and regeneration. However, limitations such as poor stability of aqueous dispersions and low accumulation in affected tissues impair the full realization of MoS2 for biomedical applications. To overcome such challenges, herein, multifunctional MoS2 -based magnetic helical microrobots (MoSBOTs) using cyanobacterium Spirulina platensis are proposed as biotemplate for therapeutic and biorecognition applications. The cytocompatible microrobots combine remote magnetic navigation with MoS2 photothermal activity under near-infrared irradiation. The resulting photoabsorbent features of the MoSBOTs are exploited for targeted photothermal ablation of cancer cells and on-the-fly biorecognition in minimally invasive oncotherapy applications. The proposed multi-therapeutic MoSBOTs hold considerable potential for a myriad of cancer treatment and diagnostic-related applications, circumventing current challenges of ablative procedures.

Remote Teaching of Chemistry Laboratory Courses during COVID-19.

This paper describes the transfer from face-to-face education to emergency remote teaching of chemistry laboratory courses in a bachelor's degree in Pharmacy during the COVID-19 pandemic. The virtualization was carried out using videos of each experimental practice and questionnaires containing the experimental data needed. The contents were integrated into the virtual platform Blackboard Collaborate, where tutorials and remote support from the teachers were provided to solve the issues raised. The didactic strategy was very positive: it turned the students into active learners, fostering knowledge sharing and promoting the self-management of their learning process. The teachers acted as guides, raising questions, and provided continuous feedback to the students that contributed to knowledge assimilation and competence acquisition. The teaching-learning process was evaluated through a rubric that graded the reports delivered by the students and a final online test. The impact of this teaching methodology was assessed by comparing the students' marks with those obtained in the conventional on-site education before the pandemic and feedback from the students via surveys. This study provides a unique experience on how a traditional instruction can be adapted to remote teaching in analytical chemistry laboratories, providing new tools that can be used in future pandemics or in other settings.

Patterned Liquid-Infused Nanocoating Integrating a Sensitive Bacterial Sensing Ability to an Antibacterial Surface.

The slippery liquid-infused surfaces show a great antibacterial property. However, most liquid-infused surfaces cannot detect whether or not the unknown aqueous samples contain microorganisms. Therefore, it is highly necessary but a challenge to integrate bacterial sensing capability into antibacterial surface. In this work, we prepared a slippery patterned liquid-infused nanocoating on the glass substrate for integrating bacterial sensing capability into the bacterial repellence surface. Dendritic mesoporous silica nanoparticles (DMSNs) with a suitable particle size of ca. 128 nm were employed as a building block to fabricate the multifunctional nanocoating with a superhydrophilic microwell and hydrophobic periphery by a dip-coating strategy, hydrophobic treatment, photomask-mediated plasma etching, and liquid infusion. Dendritic porous silica nanoparticles (DPSNs) with a larger particle size of ca. 260 nm were uniformly loaded with Au nanoparticles (NPs), providing large surface area for the modification of Raman reporter (4-mercaptobenzoic acid (4-MBA)) and aptamer. Thus, as a Raman tag, the formed DPSNs-Au-MBA-aptamer could achieve sensitive surface-enhanced Raman spectroscopy (SERS) detection of target bacteria. Combined with the Raman tag, the patterned liquid-infused nanocoating not only completely repelled bacteria on the hydrophobic area but also enabled sensitive SERS detection of Staphylococcus aureus in a very low sample volume (1 µL) with a low detection limit of 2.6 colony formation units (CFU)/mL on the antibody-modified superhydrophilic microwell. This research provided a novel and reliable strategy to construct a multifunctional nanocoating with microbial repellence and sensing capabilities.

Prussian Blue/Chitosan Micromotors with Intrinsic Enzyme-like Activity for (bio)-Sensing Assays.

Prussian Blue (PB)/chitosan enzyme mimetic tubular micromotors are used here for on-the-fly (bio)-sensing assays. The micromotors are easily prepared by direct deposition of chitosan into the pores of a membrane template and in situ PB synthesis during hydrogel deposition. Under judicious pH control, PB micromotors display enzyme mimetic capabilities with three key functions on board: the autonomous oxygen bubble propulsion (with PB acting as a catalase mimic for hydrogen peroxide decomposition), 3,3',5,5'-tetramethylbenzidine (TMB) oxidation (with PB acting as a peroxidase mimic for analyte detection), and as a magnetic material (to simplify the (bio)-sensing steps). In connection with chitosan capabilities, these unique enzyme mimetic micromotors are further functionalized with acetylthiocholinesterase enzyme (ATChE) to be explored in fast inhibition assays (20 min) for the colorimetric determination of the nerve agent neostigmine, with excellent analytical performance in terms of quantification limit (0.30 µM) and concentration linear range (up to 500 µM), without compromising efficient micromotor propulsion. The new concept illustrated holds considerable potential for a myriad of (bio)-sensing applications, including forensics, where this conceptual approach remains to be explored. Micromotor-based tests to be used in crime scenes are also envisioned due to the reliable neostigmine determination in unpretreated samples.

Transition metal dichalcogenide-based Janus micromotors for on-the-fly Salmonella detection.

Janus micromotors encapsulating transition metal dichalcogenides (TMDs) and modified with a rhodamine (RhO)-labeled affinity peptide (RhO-NFMESLPRLGMH) are used here for Salmonella enterica endotoxin detection. The OFF-ON strategy relies on the specific binding of the peptide with the TMDs to induce fluorescence quenching (OFF state); which is next recovered due to selectively binding to the endotoxin (ON state). The increase in the fluorescence of the micromotors can be quantified as a function of the concentration of endotoxin in the sample. The developed strategy was applied to the determination of Salmonella enterica serovar Typhimurium endotoxin with high sensitivity (limits of detection (LODs) of 2.0 µg/mL using MoS2, and 1.2 µg/mL using WS2), with quantitative recoveries (ranging from 93.7 ± 4.6 % to 94.3 ± 6.6%) in bacteria cultures in just 5 min. No fluorescence recovery is observed in the presence of endotoxins with a similar structure, illustrating the high selectivity of the protocol, even against endotoxins of Salmonella enterica serovar Enteritidis with great similarity in its structure, demonstrating the high bacterial specificity of the developed method. These results revealed the analytical potential of the reported strategy in multiplexed assays using different receptors or in the design of portable detection devices.

On-board smartphone micromotor-based fluorescence assays.

Herein, we describe the design of a portable device integrated with micromotors for real-time fluorescence sensing of (bio)markers. The system comprises a universal 3D printed platform to hold a commercial smartphone, which is equipped with an external magnification optical lens (20-400×) and tailor-made emission filters directly attached to the camera, an adjustable sample holder to accommodate a glass slide and laser excitation sources. On a first approach, we illustrate the suitability of the platform using magnetic Janus micromotors modified with fluorescent ZnS@CdxSe1-x quantum dots for real-time ON-OFF mercury detection. On a second approach, graphdiyne tubular catalytic micromotors modified with a rhodamine labelled affinity peptide are used for the OFF-ON detection of cholera toxin B. The micromotor-based smartphone for fluorescence sensing approach was compared to a high-performance optical microscope, and similar analytical features were obtained. This versatility allows for easy integration of micromotor fluorescence sensing strategies based on different propulsion mechanisms, allowing for its future use with a myriad of biomarkers and even multiplexed schemes.

Smartphone-Based Janus Micromotors Strategy for Motion-Based Detection of Glutathione.

Herein, we describe a Janus micromotor smartphone platform for the motion-based detection of glutathione. The system compromises a universal three-dimensional (3D)-printed platform to hold a commercial smartphone, which is equipped with an external magnification optical lens (20-400×) directly attached to the camera, an adjustable sample holder to accommodate a glass slide, and a light-emitting diode (LED) source. The presence of glutathione in peroxide-rich sample media results in the decrease in the speed of 20 µm graphene-wrapped/PtNPs Janus micromotors due to poisoning of the catalytic layer by a thiol bond formation. The speed can be correlated with the concentration of glutathione, achieving a limit of detection of 0.90 µM, with percent recoveries and excellent selectivity under the presence of interfering amino acids and proteins. Naked-eye visualization of the speed decrease allows for the design of a test strip for fast glutathione detection (30 s), avoiding previous amplification strategies or sample preparation steps. The concept can be extended to other micromotor approaches relying on fluorescence or colorimetric detection for future multiplexed schemes.

Janus particles and motors: unrivaled devices for mastering (bio)sensing.

Janus particles are a unique type of materials combining two different functionalities in a single unit. This allows the combination of different analytical properties leading to new analytical capabilities, i.e., enhanced fluid mixing to increase sensitivity with targeting capturing abilities and unique advantages in terms of multi-functionality and versatility of modification, use, and operation both in static and dynamic modes. The aim of this conceptual review is to cover recent (over the last 5 years) advances in the use of Janus microparticles and micromotors in (bio)-sensing. First, the role of different materials and synthetic routes in the performance of Janus particles are described. In a second main section, electrochemical and optical biosensing based on Janus particles and motors are covered, including in vivo and in vitro methodologies as the next biosensing generation. Current challenges and future perspectives are provided in the conclusions section.

Functional coatings enable navigation of light-propelled micromotors in blood for effective biodetoxification.

Herein we report the coating of visible light-driven polycaprolactone (PCL) based micromotors with an anti-biofouling poly lactic-co-glycolic acid (PLGA) layer for effective navigation and detoxification in blood samples. The micromotors encapsulate CdSe@ZnS quantum dots as photoresponsive materials and a Fe3O4 nanoparticle patch to promote electron transfer and reaction with glucose present in the media for diffusiophoretic propulsion in diluted blood. The coating of the micromotor with the PLGA layer prevents red blood cell adhesion and protein adsorption due to the creation of a highly efficient hydration layer. This results in an enhanced speed and efficient operation for enhanced toxin removal as compared with the bare PCL micromotors. Hemolysis and MTT assays along with no platelets aggregation revealed the high biocompatibility of the micromotors with living cells. Effective adsorptive removal of two relevant toxins, sepsis associated Escherichia coli O111:B4 toxin and snake venom α-bungarotoxin from blood is achieved with the PLGA micromotors. The new developments illustrated here represent one step forward in the use of light-driven micromotors for biomedical applications.

Peroxidase driven micromotors for dynamic bioremediation.

Phenolics are size products present in tons concentrations in industrial wastewater that can cause adverse health effects when released in the environment. As such, there is a growing interest in the development of efficient strategies for the removal of phenolic compounds from polluted water. Herein we describe the use of poly(3,4-ethylenedioxythiophene) (PEDOT)-Au/peroxidase micromotors as dynamic biocatalytic platforms for the removal of model phenolics (phenol, bisphenol A, guaiacol, pyrogallol and catechol). Micromotors are synthetized by using a simplified template electrodeposition protocol followed by covalent enzyme immobilization in the inner Au layer. Kinetic parameters revealed that enzyme immobilization in the inner micromotor layer increased over 2-fold the enzymatic activity, along with increasing operational pH and thermal stabilities. The micromotors can propel at speed of up to 60 µm/s, generating an enhanced fluid mixing that results in removal efficiencies of up to 60% as compared with the 27% removal when using free peroxidase under the same conditions. In addition, excellent activities of almost 100% were obtained within ten cycles of removal using the micromotors. This newly developed bioremediation strategy holds considerable promise in for its application in large scale water treatment systems and many relevant environmental processes.

Dual-Propelled Lanbiotic Based Janus Micromotors for Selective Inactivation of Bacterial Biofilms.

Graphene oxide/PtNPs/Fe2 O3 "dual-propelled" catalytic and fuel-free rotary actuated magnetic Janus micromotors modified with the lanbiotic Nisin are used for highly selective capture/inactivation of gram-positive bacteria units and biofilms. Specific interaction of Nisin with the Lipid II unit of Staphylococcus Aureus bacteria in connection with the enhanced micromotor movement and generated fluid flow result in a 2-fold increase of the capture/killing ability (both in bubble and magnetic propulsion modes) as compared with free peptide and static counterparts. The high stability of Nisin along with the high towing force of the micromotors allow for efficient operation in untreated raw media (tap water, juice and serum) and even in blood and in flowing blood in magnetic mode. The high selectivity of the approach is illustrated by the dramatically lower interaction with gram-negative bacteria (Escherichia Coli). The double-propulsion (catalytic or fuel-free magnetic) mode of the micromotors and the high biocompatibility holds considerable promise to design micromotors with tailored lanbiotics that can response to the changes that make the bacteria resistant in a myriad of clinical, environmental remediation or food safety applications.

Janus Micromotors Coated with 2D Nanomaterials as Dynamic Interfaces for (Bio)-Sensing.

In this work, we study the interaction of graphdiyne oxide (GDYO)-, graphene oxide (GO)-, or black phosphorous (BP)-wrapped Janus micromotors using a model system relying on a fluorescence-labeled affinity peptide, which is released upon specific interaction with a target Cholera Toxin B. Such ON-OFF-ON system allows mimicking similar processes occurring at (bio)-interfaces and to study the related sorption and desorption kinetics. The distinct surface properties of each nanomaterial play a critical role in the loading/release capacity of the peptide, greatly influencing the release profiles. Sorption obeys a second-order kinetic model using the two-dimensional (2D) nanomaterials in connection with micromotors, indicating a strong influence of chemisorption process for BP micromotors. Yet, release kinetics are faster for GDYO and GO nanomaterials, indicating a contribution of π and hydrophobic interactions in the probe sorption (Cholera Toxin B affinity peptide) and target probe release (in the presence of Cholera Toxin B). Micromotor movement also plays a critical role in such processes, allowing for efficient operation in low raw sample volumes, where the high protein content can diminish probe loading/release, affecting the overall performance. The loading/release capacity and feasibility of the (bio)-sensing protocol are illustrated in Vibrio cholerae and Vibrio parahaemolyticus bacteria cultures as realistic domains. The new concept described here holds considerable promise to understand the interaction of micromotor with biological counterparts in a myriad of biomedical and other practical applications, including the design of novel micromotor-based sensors.

Light-driven nanomotors and micromotors: envisioning new analytical possibilities for bio-sensing.

The aim of this conceptual review is to cover recent developments of light-propelled micromotors for analytical (bio)-sensing. Challenges of self-propelled light-driven micromotors in complex (biological) media and potential solutions from material aspects and propulsion mechanism to achieve final analytical detection for in vivo and in vitro applications will be comprehensively covered. Graphical abstract.