Showing papers in "Nature Nanotechnology in 2012"
TL;DR: This work reviews the historical development of Transition metal dichalcogenides, methods for preparing atomically thin layers, their electronic and optical properties, and prospects for future advances in electronics and optoelectronics.
Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.
13,348 citations
TL;DR: It is demonstrated that optical pumping with circularly polarized light can achieve complete dynamic valley polarization in monolayer MoS(2) (refs 11, 12), a two-dimensional non-centrosymmetric crystal with direct energy gaps at two valleys.
Abstract: Circularly polarized light has been used to confine charge carriers in single-layer molybdenum disulphide entirely to a single energy-band valley, representing full valley polarization.
3,425 citations
TL;DR: It is demonstrated that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS(2), demonstrating the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS (2) monolayers.
Abstract: Most electronic devices exploit the electric charge of electrons, but it is also possible to build devices that rely on other properties of electrons. Spintronic devices, for example, make use of the spin of electrons. Valleytronics is a more recent development that relies on the fact that the conduction bands of some materials have two or more minima at equal energies but at different positions in momentum space. To make a valleytronic device it is necessary to control the number of electrons in these valleys, thereby producing a valley polarization. Single-layer MoS(2) is a promising material for valleytronics because both the conduction and valence band edges have two energy-degenerate valleys at the corners of the first Brillouin zone. Here, we demonstrate that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS(2). Our results, and similar results by Mak et al., demonstrate the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS(2) monolayers.
3,158 citations
TL;DR: The rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups are discussed.
Abstract: Nanodiamonds have excellent mechanical and optical properties, high surface areas and tunable surface structures. They are also non-toxic, which makes them well suited to biomedical applications. Here we review the synthesis, structure, properties, surface chemistry and phase transformations of individual nanodiamonds and clusters of nanodiamonds. In particular we discuss the rational control of the mechanical, chemical, electronic and optical properties of nanodiamonds through surface doping, interior doping and the introduction of functional groups. These little gems have a wide range of potential applications in tribology, drug delivery, bioimaging and tissue engineering, and also as protein mimics and a filler material for nanocomposites.
2,351 citations
TL;DR: The basic concept of the nanoparticle corona is reviewed and its structure and composition is highlighted, and how the properties of the corona may be linked to its biological impacts are highlighted.
Abstract: The search for understanding the interactions of nanosized materials with living organisms is leading to the rapid development of key applications, including improved drug delivery by targeting nanoparticles, and resolution of the potential threat of nanotechnological devices to organisms and the environment. Unless they are specifically designed to avoid it, nanoparticles in contact with biological fluids are rapidly covered by a selected group of biomolecules to form a corona that interacts with biological systems. Here we review the basic concept of the nanoparticle corona and its structure and composition, and highlight how the properties of the corona may be linked to its biological impacts. We conclude with a critical assessment of the key problems that need to be resolved in the near future.
2,245 citations
TL;DR: It is shown that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity.
Abstract: Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).
2,133 citations
TL;DR: A gain of ∼10(8) electrons per photon and a responsivity of ∼ 10(7) A W(-1) in a hybrid photodetector that consists of monolayer or bilayer graphene covered with a thin film of colloidal quantum dots is demonstrated.
Abstract: A phototransistor in which electric charges are absorbed by colloidal quantum dots and circulated in graphene exhibits high values for gain, responsivity and specific detectivity.
1,921 citations
TL;DR: It is shown that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions.
Abstract: Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.
1,471 citations
TL;DR: This work describes a composite material composed of a supramolecular organic polymer with embedded nickel nanostructured microparticles, which shows mechanical and electrical self-healing properties at ambient conditions and shows that the material is pressure- and flexion-sensitive, and therefore suitable for electronic skin applications.
Abstract: Pressure sensitivity and mechanical self-healing are two vital functions of the human skin. A flexible and electrically conducting material that can sense mechanical forces and yet be able to self-heal repeatably can be of use in emerging fields such as soft robotics and biomimetic prostheses, but combining all these properties together remains a challenging task. Here, we describe a composite material composed of a supramolecular organic polymer with embedded nickel nanostructured microparticles, which shows mechanical and electrical self-healing properties at ambient conditions. We also show that our material is pressure- and flexion-sensitive, and therefore suitable for electronic skin applications. The electrical conductivity can be tuned by varying the amount of nickel particles and can reach values as high as 40 S cm−1. On rupture, the initial conductivity is repeatably restored with ∼90% efficiency after 15 s healing time, and the mechanical properties are completely restored after ∼10 min. The composite resistance varies inversely with applied flexion and tactile forces. These results demonstrate that natural skin's repeatable self-healing capability can be mimicked in conductive and piezoresistive materials, thus potentially expanding the scope of applications of current electronic skin systems. A supramolecular polymer with embedded nanostructured Ni particles shows mechanical and electrical self-healing capabilities as well as piezoresistive properties, making it a good candidate for electronic skin applications.
1,240 citations
TL;DR: The density of midgap trap states in CQD solids is quantified and shown to be limited by electron-hole recombination due to these states, and a robust hybrid passivation scheme is developed that can passivate trap sites that are inaccessible to much larger organic ligands.
Abstract: Improved performance in a photovoltaic device made of colloidal quantum dots is achieved through a combination of passivation by halide anions and organic crosslinking.
1,183 citations
IBM1
TL;DR: Transparent photonic devices based on graphene/insulator stacks, which are formed by depositing alternating wafer-scale graphene sheets and thin insulating layers, then patterning them together into photonic-crystal-like structures are demonstrated, showing experimentally that the plasmon in such stacks is unambiguously non-classical.
Abstract: The collective oscillation of carriers--the plasmon--in graphene has many desirable properties, including tunability and low loss. However, in single-layer graphene, the dependence on carrier concentration of both the plasmonic resonance frequency and magnitude is relatively weak, limiting its applications in photonics. Here, we demonstrate transparent photonic devices based on graphene/insulator stacks, which are formed by depositing alternating wafer-scale graphene sheets and thin insulating layers, then patterning them together into photonic-crystal-like structures. We show experimentally that the plasmon in such stacks is unambiguously non-classical. Compared with doping in single-layer graphene, distributing carriers into multiple graphene layers effectively enhances the plasmonic resonance frequency and magnitude, which is different from the effect in a conventional semiconductor superlattice and is a direct consequence of the unique carrier density scaling law of the plasmonic resonance of Dirac fermions. Using patterned graphene/insulator stacks, we demonstrate widely tunable far-infrared notch filters with 8.2 dB rejection ratios and terahertz linear polarizers with 9.5 dB extinction ratios. An unpatterned stack consisting of five graphene layers shields 97.5% of electromagnetic radiation at frequencies below 1.2 THz. This work could lead to the development of transparent mid- and far-infrared photonic devices such as detectors, modulators and three-dimensional metamaterial systems.
TL;DR: It is shown that ultraviolet-induced oxidative etching can create pores in micrometre-sized graphene membranes, and the resulting membranes can be used as molecular sieves and agree with models based on effusion through a small number of ångstrom-sized pores.
Abstract: Membranes act as selective barriers and play an important role in processes such as cellular compartmentalization and industrial-scale chemical and gas purification. The ideal membrane should be as thin as possible to maximize flux, mechanically robust to prevent fracture, and have well-defined pore sizes to increase selectivity. Graphene is an excellent starting point for developing size-selective membranes because of its atomic thickness, high mechanical strength, relative inertness and impermeability to all standard gases. However, pores that can exclude larger molecules but allow smaller molecules to pass through would have to be introduced into the material. Here, we show that ultraviolet-induced oxidative etching can create pores in micrometre-sized graphene membranes, and the resulting membranes can be used as molecular sieves. A pressurized blister test and mechanical resonance are used to measure the transport of a range of gases (H(2), CO(2), Ar, N(2), CH(4) and SF(6)) through the pores. The experimentally measured leak rate, separation factors and Raman spectrum agree well with models based on effusion through a small number of angstrom-sized pores.
TL;DR: This unprecedented level of sensitivity allows us to detect adsorption events of naphthalene molecules, and to measure the binding energy of a xenon atom on the nanotube surface, which could have applications in mass spectrometry, magnetometry and surface science.
Abstract: A carbon nanotube resonator is used to form the basis of an ultrasensitive mass sensor that can also be employed to study basic phenomena in surface science.
TL;DR: In this paper, a tetrahedral DNA strand self-assembles into tetrahedron nanoparticles that can deliver small interfering RNA molecules to cells and suppress genes in tumours.
Abstract: DNA strands can self-assemble into tetrahedral nanoparticles that can deliver small interfering RNA molecules to cells and suppress genes in tumours.
TL;DR: A method is reported for creating hybrid organic-inorganic nanoflowers using copper (II) ions as the inorganic component and various proteins as the organic component to exhibit enhanced enzymatic activity and stability compared with the free enzyme.
Abstract: Flower-shaped inorganic nanocrystals(1-3) have been used for applications in catalysis(4,5) and analytical science(6,7), but so far there have been no reports of 'nanoflowers' made of organic components(8). Here, we report a method for creating hybrid organic-inorganic nanoflowers using copper (II) ions as the inorganic component and various proteins as the organic component. The protein molecules form complexes with the copper ions, and these complexes become nucleation sites for primary crystals of copper phosphate. Interaction between the protein and copper ions then leads to the growth of micrometre-sized particles that have nanoscale features and that are shaped like flower petals. When an enzyme is used as the protein component of the hybrid nanoflower, it exhibits enhanced enzymatic activity and stability compared with the free enzyme. This is attributed to the high surface area and confinement of the enzymes in the nanoflowers.
TL;DR: In this paper, the authors showed that repairing the abnormal vessels in mammary tumours, by blocking vascular endothelial growth factor receptor-2, improves the delivery of smaller nanoparticles (diameter, 12 nm) while hindering delivery of larger nanoparticles, and further suggest that smaller (∼12 nm) nanomedicines are ideal for cancer therapy due to their superior tumour penetration.
Abstract: The blood vessels of cancerous tumours are leaky and poorly organized. This can increase the interstitial fluid pressure inside tumours and reduce blood supply to them, which impairs drug delivery. Anti-angiogenic therapies--which 'normalize' the abnormal blood vessels in tumours by making them less leaky--have been shown to improve the delivery and effectiveness of chemotherapeutics with low molecular weights, but it remains unclear whether normalizing tumour vessels can improve the delivery of nanomedicines. Here, we show that repairing the abnormal vessels in mammary tumours, by blocking vascular endothelial growth factor receptor-2, improves the delivery of smaller nanoparticles (diameter, 12 nm) while hindering the delivery of larger nanoparticles (diameter, 125 nm). Using a mathematical model, we show that reducing the sizes of pores in the walls of vessels through normalization decreases the interstitial fluid pressure in tumours, thus allowing small nanoparticles to enter them more rapidly. However, increased steric and hydrodynamic hindrances, also associated with smaller pores, make it more difficult for large nanoparticles to enter tumours. Our results further suggest that smaller (∼12 nm) nanomedicines are ideal for cancer therapy due to their superior tumour penetration.
TL;DR: It is shown using an indentation-type atomic force microscope (IT-AFM) that unadulterated human breast biopsies display distinct stiffness profiles, and evidence obtained from the lungs of mice with late-stage tumours shows that migration and metastatic spreading is correlated to the low stiffness of hypoxia-associated cancer cells.
Abstract: Cancer initiation and progression follow complex molecular and structural changes in the extracellular matrix and cellular architecture of living tissue. However, it remains poorly understood how the transformation from health to malignancy alters the mechanical properties of cells within the tumour microenvironment. Here, we show using an indentation-type atomic force microscope (IT-AFM) that unadulterated human breast biopsies display distinct stiffness profiles. Correlative stiffness maps obtained on normal and benign tissues show uniform stiffness profiles that are characterized by a single distinct peak. In contrast, malignant tissues have a broad distribution resulting from tissue heterogeneity, with a prominent low-stiffness peak representative of cancer cells. Similar findings are seen in specific stages of breast cancer in MMTV-PyMT transgenic mice. Further evidence obtained from the lungs of mice with late-stage tumours shows that migration and metastatic spreading is correlated to the low stiffness of hypoxia-associated cancer cells. Overall, nanomechanical profiling by IT-AFM provides quantitative indicators in the clinical diagnostics of breast cancer with translational significance.
TL;DR: By identifying the regimes of junction doping concentration in which each mechanism dominates, this work was able to design and fabricate an independently confirmed 18.2%-efficient nanostructured 'black-silicon' cell that does not need the antireflection coating layer normally required to reach a comparable performance level.
Abstract: The efficiency of solar cells with high-area, nanostructured surfaces is limited by surface and Auger charge-recombination processes, which can be slowed through appropriate levels of junction doping
TL;DR: This work presents atomic-scale images and electronic characteristics of these atomically precise devices and the impact of strong vertical and lateral confinement on electron transport and discusses the opportunities ahead for atomic- scale quantum computing architectures.
Abstract: The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunnelling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices-such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices-requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy.
TL;DR: The colour-mapping strategy produces images with both sharp colour changes and fine tonal variations, is amenable to large-volume colour printing via nanoimprint lithography, and could be useful in making microimages for security, steganography, nanoscale optical filters and high-density spectrally encoded optical data storage.
Abstract: Controlling the plasmon resonance of nanodisk structures enables colour images to be printed at the ultimate resolution of 100,000 dots per inch, as viewed by bright-field microscopy.
TL;DR: A conductive composite mat of silver nanoparticles and rubber fibres that allows the formation of highly stretchable circuits through a fabrication process that is compatible with any substrate and scalable for large-area applications is introduced.
Abstract: A highly stetchable non-woven mat with printed conductive circuits is fabricated by embedding silver nanoparticles in electrospun fibres.
TL;DR: A signal generation mechanism for biosensing is introduced that enables the detection of a few molecules of analyte with the naked eye in whole serum at the ultralow concentration of 1 × 10(-18) g ml(-1).
Abstract: A new signal generation mechanism based on the growth of gold nanoparticles offers a way to detect ultralow concentrations of analytes with the naked eye.
TL;DR: A robust method for scanning a single nitrogen-vacancy centre within tens of nanometres from a sample surface that addresses both of these concerns is demonstrated, and is able to image magnetic domains with widths of 25 nm, and demonstrate a magnetic field sensitivity of 56 nT Hz(-1/2) at a frequency of 33 kHz, which is unprecedented for scanning nitrogen-Vacancy centres.
Abstract: The nitrogen-vacancy defect centre in diamond has potential applications in nanoscale electric and magnetic-field sensing, single-photon microscopy, quantum information processing and bioimaging. These applications rely on the ability to position a single nitrogen-vacancy centre within a few nanometres of a sample, and then scan it across the sample surface, while preserving the centre's spin coherence and readout fidelity. However, existing scanning techniques, which use a single diamond nanocrystal grafted onto the tip of a scanning probe microscope, suffer from short spin coherence times due to poor crystal quality, and from inefficient far-field collection of the fluorescence from the nitrogen-vacancy centre. Here, we demonstrate a robust method for scanning a single nitrogen-vacancy centre within tens of nanometres from a sample surface that addresses both of these concerns. This is achieved by positioning a single nitrogen-vacancy centre at the end of a high-purity diamond nanopillar, which we use as the tip of an atomic force microscope. Our approach ensures long nitrogen-vacancy spin coherence times (∼75 µs), enhanced nitrogen-vacancy collection efficiencies due to waveguiding, and mechanical robustness of the device (several weeks of scanning time). We are able to image magnetic domains with widths of 25 nm, and demonstrate a magnetic field sensitivity of 56 nT Hz(-1/2) at a frequency of 33 kHz, which is unprecedented for scanning nitrogen-vacancy centres.
TL;DR: The plasmonic detection of single molecules in real time without the need for labelling or amplification is reported, and the binding of single proteins is detected by monitoring the plAsmon resonance of the nanorod with a sensitive photothermal assay.
Abstract: Existing methods for the optical detection of single molecules require the molecules to absorb light to produce fluorescence or direct absorption signals. This limits the range of species that can be detected, because most molecules are purely refractive. Metal nanoparticles or dielectric resonators can be used to detect non-absorbing molecules because local changes in the refractive index produce a resonance shift. However, current approaches only detect single molecules when the resonance shift is amplified by a highly polarizable label or by a localized precipitation reaction on the surface of a nanoparticle. Without such amplification, single-molecule events can only be identified in a statistical way. Here, we report the plasmonic detection of single molecules in real time without the need for labelling or amplification. Our sensor consists of a single gold nanorod coated with biotin receptors, and the binding of single proteins is detected by monitoring the plasmon resonance of the nanorod with a sensitive photothermal assay. The sensitivity of our device is ∼700 times higher than state-of-the-art plasmon sensors and is intrinsically limited by spectral diffusion of the surface plasmon resonance.
TL;DR: A simple solution method is used to prepare emissive hybrid quantum dots consisting of a ZnO core wrapped in a shell of single-layer graphene to make a white-light-emitting diode, and two additional blue emission peaks are observed in the luminescent spectrum of the quantum dot.
Abstract: Quantum dots with a zinc oxide core and a strained graphene shell are used as an emissive layer in a white-light-emitting diode.
TL;DR: It is shown that a solution-processed ultraviolet photodetector with a nanocomposite active layer composed of ZnO nanoparticles blended with semiconducting polymers can significantly outperform inorganicPhotodetectors.
Abstract: A solution-processed ultraviolet photodetector with a nanocomposite active layer composed of ZnO nanoparticles blended with semiconducting polymers can significantly outperform inorganic photodetectors
TL;DR: In this article, magnetoferritin nanoparticles (M-HFn) are used to target and visualize tumour tissues without the use of any targeting ligands or contrast agents, which can distinguish cancerous cells from normal cells with a sensitivity of 98% and specificity of 95%.
Abstract: Engineered nanoparticles have been used to provide diagnostic, therapeutic and prognostic information about the status of disease. Nanoparticles developed for these purposes are typically modified with targeting ligands (such as antibodies, peptides or small molecules) or contrast agents using complicated processes and expensive reagents. Moreover, this approach can lead to an excess of ligands on the nanoparticle surface, and this causes non-specific binding and aggregation of nanoparticles, which decreases detection sensitivity. Here, we show that magnetoferritin nanoparticles (M-HFn) can be used to target and visualize tumour tissues without the use of any targeting ligands or contrast agents. Iron oxide nanoparticles are encapsulated inside a recombinant human heavy-chain ferritin (HFn) protein shell, which binds to tumour cells that overexpress transferrin receptor 1 (TfR1). The iron oxide core catalyses the oxidation of peroxidase substrates in the presence of hydrogen peroxide to produce a colour reaction that is used to visualize tumour tissues. We examined 474 clinical specimens from patients with nine types of cancer and verified that these nanoparticles can distinguish cancerous cells from normal cells with a sensitivity of 98% and specificity of 95%.
TL;DR: In this article, the authors highlight the advances in microfluidic systems that can synthesize libraries of nanoparticles in a well-controlled, reproducible and high-throughput manner.
Abstract: Using nanoparticles for therapy and imaging holds tremendous promise for the treatment of major diseases such as cancer. However, their translation into the clinic has been slow because it remains difficult to produce nanoparticles that are consistent 'batch-to-batch', and in sufficient quantities for clinical research. Moreover, platforms for rapid screening of nanoparticles are still lacking. Recent microfluidic technologies can tackle some of these issues, and offer a way to accelerate the clinical translation of nanoparticles. In this Progress Article, we highlight the advances in microfluidic systems that can synthesize libraries of nanoparticles in a well-controlled, reproducible and high-throughput manner. We also discuss the use of microfluidics for rapidly evaluating nanoparticles in vitro under microenvironments that mimic the in vivo conditions. Furthermore, we highlight some systems that can manipulate small organisms, which could be used for evaluating the in vivo toxicity of nanoparticles or for drug screening. We conclude with a critical assessment of the near- and long-term impact of microfluidics in the field of nanomedicine.
TL;DR: Although cells in different phases of the cell cycle were found to internalize nanoparticles at similar rates, after 24 h the concentration of nanoparticles in the cells could be ranked according to the different phases: G2/M > S > G0/G1.
Abstract: Nanoparticles are considered a primary vehicle for targeted therapies because they can pass biological barriers and enter and distribute within cells by energy-dependent pathways. So far, most studies have shown that nanoparticle properties, such as size and surface, can influence how cells internalize nanoparticles. Here, we show that uptake of nanoparticles by cells is also influenced by their cell cycle phase. Although cells in different phases of the cell cycle were found to internalize nanoparticles at similar rates, after 24 h the concentration of nanoparticles in the cells could be ranked according to the different phases: G2/M > S > G0/G1. Nanoparticles that are internalized by cells are not exported from cells but are split between daughter cells when the parent cell divides. Our results suggest that future studies on nanoparticle uptake should consider the cell cycle, because, in a cell population, the dose of internalized nanoparticles in each cell varies as the cell advances through the cell cycle.
TL;DR: It is shown that time-resolved tip-enhanced Raman spectroscopy can monitor photocatalytic reactions at the nanoscale and can be used to observe other molecular effects such as monolayer diffusion.
Abstract: Heterogeneous catalysts play a pivotal role in the chemical industry, but acquiring molecular insights into functioning catalysts remains a significant challenge. Recent advances in micro-spectroscopic approaches have allowed spatiotemporal information to be obtained on the dynamics of single active sites and the diffusion of single molecules. However, these methods lack nanometre-scale spatial resolution and/or require the use of fluorescent labels. Here, we show that time-resolved tip-enhanced Raman spectroscopy can monitor photocatalytic reactions at the nanoscale. We use a silver-coated atomic force microscope tip to both enhance the Raman signal and to act as the catalyst. The tip is placed in contact with a self-assembled monolayer of p-nitrothiophenol molecules adsorbed on gold nanoplates. A photocatalytic reduction process is induced at the apex of the tip with green laser light, while red laser light is used to monitor the transformation process during the reaction. This dual-wavelength approach can also be used to observe other molecular effects such as monolayer diffusion.