Nanoscale Investigation Research Articles

Manganese-Doped Carbon Dots as a Promising Nanoprobe for Luminescent and Magnetic Resonance Imaging

Luminescent carbon nanodots (CDs) are a low-toxic nanomaterial with a tunable emission in a wide spectral range and with various functional groups on the surface. Therefore, CDs can prospectively serve as luminescent nanoprobes for biomedical applications, such as drug-delivery, visualization, sensing, etc. The doping of CDs with paramagnetic or transition metals allows the expansion of the range of applications of CDs and the fabrication of a multimodal nanoprobe for bioimaging. Here, we developed CDs doped with manganese (Mn) based on commonly used precursors—o-phenylenediamine or citric acid and formamide. The chemical structure, morphology, optical properties, and magnetic resonance responses have been carefully studied. The obtained CDs are up to 10 nm, with emissions observed in the 400–650 nm spectral region. CDs exhibit an ability to reduce both T1 and T2 relaxation times by up to 6.4% and 42.3%, respectively. The high relaxivity values suggest the use of CDs as promising dual-mode contrast agents for T1 and T2 MRI. Therefore, our developed CDs can be utilized as a new multifunctional nanoscale probe for photoluminescent and magnetic resonance bioimaging.

Label-free, ultra-low detection limit DNA biosensor using high quality optical microcavity functionalized by DNA tetrahedral nanostructure probes.

This study proposes and demonstrates a novel label-free DNA biosensor using high quality optical microcavity functionalized by 3D DNA nanostructure probes. To achieve ultra-low limit DNA biosensing, optical sensing interface of the hollow-core, thin wall-thickness microcavity was functionalized by self-assembled DNA tetrahedral nanostructure (DTN) probes with size of 17 bp and length of ∼5.8 nm. High efficiency binding of the DTN probes with the optical sensor interface and the target ssDNA are achieved. Whispering gallery mode (WGM) spectra with high-Q factor of >107 are excited and traced for DNA detection inside the microfluidic channel of the microcavity, with a small sample volume of nL. Incorporation of nanoscale DTN probes onto surface of the optical microcavity makes it an effective way for increasing efficient probe density and eliminating entanglement between DNA probes, thus ∼1000 times lower detection limit is achieved as compared to using 1D ssDNA probes. Due to its desirable merits of label-free, ultra-low LoD, real time and compact size, the proposed DNA biosensor has broad application prospects in bioengineering and medical diagnosis.

Local Photochemical Nanoscopy of Hot-Carrier-Driven Catalytic Reactions Using Plasmonic Nanosystems.

Nanoscale investigation of the reactivity of photocatalytic systems is crucial for their fundamental understanding and improving their design and applicability. Here, we present a photochemical nanoscopy technique that unlocks the local spatial detection of molecular products during plasmonic hot-carrier-driven photocatalytic reactions with nanometric precision. By applying the methodology to Au/TiO2 plasmonic photocatalysts, we experimentally and theoretically determined that smaller and denser Au nanoparticle arrays present lower optical contribution with quantum efficiency in hot-hole-driven photocatalysis closely related to the population heterogeneity. As expected, the highest quantum yield from a redox probe oxidation is achieved at the plasmon peak. Investigating a single plasmonic nanodiode, we unravel the areas where oxidation and reduction products are evolved with subwavelength resolution (∼200 nm), illustrating the bipolar behavior of such nanosystems. These results open the way to quantitative investigations at the nanoscale to evaluate the photocatalytic reactivity of low-dimensional materials in a variety of chemical reactions.

Genetic Targeting of Solvatochromic Dyes for Probing Nanoscale Environments of Proteins in Organelles.

A variety of protein tags are available for genetically encoded protein labeling, which allow their precise localization and tracking inside the cells. A new dimension in protein imaging can be offered by combining protein tags with polarity-sensitive fluorescent probes, which provide information about local nanoscale environments of target proteins within the subcellular compartments (organelles). Here, we designed three fluorescent probes based on solvatochromic nile red dye, conjugated to a HaloTag reactive targeting group through polyethylene glycol linkers of varying lengths. The probe with medium linker length, NR12-Halo, was found to label specifically a large variety of proteins localized in defined cell compartments, such as plasma membranes (outer and inner leaflets), endoplasmic reticulum, Golgi apparatus, cytosol, microtubules, actin, and chromatin. Owing to its polarity-sensitive fluorophore, the probe clearly distinguished the proteins localized within apolar lipid membranes from other proteins. Moreover, it revealed dramatic changes in the environment during the life cycle of proteins from biosynthesis to their expected localization and, finally, to recycling inside lysosomes. Heterogeneity in the local polarity of some membrane proteins also suggested a formation of low-polar protein aggregates, for example, within cell-cell contacts. The approach also showed that mechanical stress (cell shrinking by osmotic shock) induced a general polarity decrease in membrane proteins, probably due to the condensation of biomolecules. Finally, the nanoenvironment of some membrane proteins was affected by a polyunsaturated fatty acid diet, which provided the bridge between organization of lipids and proteins. The developed solvatochromic HaloTag probe constitutes a promising tool for probing nanoscale environments of proteins and their interactions within subcellular structures.

Nanoscale investigation on electric field induced ferroelectric phase transitions in the rhombohedral PMN-PT single crystal

The excellent piezoelectric property of Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) single crystals has attracted increasing attentions for their application in electromechanical devices. Generally, the electric field induced phase transition is an important contribution to the piezoelectric response. Understanding the pathway of electric field induced phase transition is essential for the practical application of PMN-PT crystals. Here, evolution of the domain structure and surface screening charges during phase transitions in the (001) oriented 0.72PMN-0.28PT crystal were studied at nanoscale via piezo-response force microscopy (PFM) and Kelvin probe force microscopy (KPFM). In combination with confocal polarized Raman spectroscopy, electric field induced phase transitions were locally studied. PFM tip bias poling in 0.72PMN-0.28PT single crystal results in a rhombohedral to monoclinic phase transition. And the monoclinic phase relaxes back to the rhombohedral at elevated temperatures. Our work provides nanoscale investigations on the electric field induced phase transition, and will be instructive for the practical application of PMN-PT single crystals.

Nanoscale local modification of PMMA refractive index by tip-enhanced femtosecond pulsed laser irradiation

Tip-enhanced optical effects have enabled a wide palette of nanoscale investigation techniques and recently they were successfully used to modify and manipulate matter with nanoscale spatial resolution. We contribute to this latter area by reporting a viable method to modify the refractive index of polymethyl methacrylate (PMMA). Local surface changes of the refractive index are accomplished by focusing a femtosecond pulsed near-infrared laser beam on the apex of a metalized nanosized tip, traditionally used in scanning probe microscopy (SPM). The refractive index is changed over a circular area with diameter <200 nm under 790 nm illumination, representing a four-fold increase in resolution compared to the current state-of-the-art. These results are obtained at low laser pulse energies (<0.5 nJ), which represents a two orders of magnitude advantage over previously reported methods. Besides enabling modifications of the refractive index with high lateral resolution, this method can pave the way towards other important applications such the fabrication of photonic crystal lattices and surface waveguides.

Macroscopic and nanoscale investigation of the enhanced wear properties of medium-Mn steel processed via room-temperature quenching and partitioning

High-manganese austenitic and high hardness martensitic steels are widely used in wear-related applications. However, their abrasive wear performance is unsatisfactory because of the insufficient twinning induced plasticity effect of the former and the weak strain hardening and low crack resistance during wear of the latter. Here, novel wear-resistant steels were developed via alloy design and simple room-temperature quenching and partitioning (RT-Q&P) of medium Mn steels (0.3C–10Mn and 0.3C–10Mn-0.25V). Their microstructure and sliding abrasive wear behavior were compared to those of conventional Hardox400 and Hadfield steels. The two medium-Mn steels had better wear properties than conventional wear-resistant steels. Moreover, the V-containing steel with a multiphase microstructure of tempered martensite, retained austenite, and nano-vanadium carbide precipitates, possessed 2.98 and 3.45 times higher abrasive wear resistance than the Hardox400 and Hadfield steels, respectively. Besides the stimulated transformation-induced-plasticity effect in RT-Q&P steels, the enhanced abrasive wear resistance of V-containing steel was attributed to microstructural refinement and improved strain hardening during wear imparted by V element. The main wear mechanism of RT-Q&P wear-resistant steels was cutting, while it was grooves and pits for Hadfield steel, and peeling pits and delamination for Hardox400 steel. This study can guide the design of structural materials with excellent wear resistance through multiphase microstructural and nano-precipitate regulation to overcome the wear challenges of components.

Growth of Magnetron-Sputtered Ultrathin Chromium Films: In Situ Monitoring and Ex Situ Film Properties

We report a systematic nanoscale investigation on the ultrathin Cr film growth process and properties. Polycrystalline metallic films were manufactured by magnetron sputtering on fused silica substrates. The film growth was observed in situ by broad-band optical monitoring (BBM) and plasma-emission spectroscopy (OES) methods. The ex situ characterization of the Cr films with thicknesses varying from 2.6 nm up to 57 nm were performed by both non-destructive and destructive techniques. Recently, we reported on a novel set of data for optical and electrical properties of sputtered chromium films. The optical and electrical properties of the films are known to be governed by their structure and microstructure, which were analyzed in detail in the present research. Moreover, the optical properties of the films were studied here in a significantly wider optical range and obtained using both in situ and ex situ measurements. Reliable in situ nanoscale characterization of metal films was shown to ensure an unfailing approach in obtaining ultrathin layers with desirable thickness and stable and well-determined optical constants and electrical conductivity. This is of high importance for various industries and novel upcoming applications.

Theoretical and experimental investigation of solubility and Young's modulus models for polyhydroxybutyrate‐based electrospun scaffolds

AbstractOver the past decades, limited strategies have been developed to study nanomechanical properties. The in‐depth study on the nanomechanical properties of electrospun scaffolds can provide better insights at greater scales. Atomic force microscopy (AFM) nanoindentation is an authoritative method that can characterize mechanical properties. In this research, theoretical solubility studies of polyhydroxybutyrate (PHB) in different solvents were initially carried out. Then, three series of PHB‐based mats were prepared, including PHB/lignin, PHB/cellulose nanofiber (CNF), and PHB/lignin/CNF. The theoretical modulus of samples was studied from two different standpoints, through the use of nanoindentation on a single nanofiber. First, scaffolds were considered as a series of short fiber reinforced nanocomposites (NCs). In the second viewpoint, the geometrical structure of each scaffold was considered similar to an open‐cell foam (OCF). Consequently, modeling outputs verified that among NC models, isotropic Halpin‐Tsai presented plausible predictions with ≃93.36 to 99.77% accuracy. In addition, Tetrakaidecahedron indicated more accurate predictions among OCF models for the mats (≃78.99 to 96.15% adaption). Indeed, the theoretical NC and OCF models were able to provide acceptable forecasts for the application range of electrospun fibers. Based on this, nanoscale investigation of mechanical properties can turn a new page to estimate the further application of mats.

Thermal and acoustic insulation properties in nanoporous geopolymer nanocomposite

In building and construction sector, seeking for high thermal and sound insulation materials is crucial to reach lower carbon footprints and also for curtailed consumption energy either for heating or for cooling. Nowadays, geopolymer nanocomposites, an alternative binder to Ordinary Portland Cement (OPC), are drawing considerable attention for their great prospective to withstand heat and sound exposure beside to their outstanding properties including high early strength, little creep and shrinkage and a good resistance to corrosion and abrasion. To advance geopolymer insulating properties, a nanoscale analysis has been investigated here to consider porosity, nanopore size, moisture as well as chemical composition and alkali agents impacts. Our findings conclude that a better thermal isolation is predicted for a high-silicon content geopolymer nanostructure with the presence of sodium alkali activators. The lowest thermal conductivity values of 0.08 W/m.K and 0.10 W/m.K are obtained for a porosity of 30.8% for Na+ and K+ samples, respectively. Considering humidity, results indicate that residual water enhances 4.5 times the thermal insulation of a highly nanoporous metakaolin geopolymer rich on silicon and in the presence of NaOH alkali activator. Nanoscale investigation has finally shown a promising acoustic insulation behavior than OPC material when pore size and porosity are higher than 12 Å and 20% respectively, making nanoporous geopolymer paste as a great challenge for cementitious materials.

Heat-Driven Iontronic Nanotransistors.

Thermoelectric polyelectrolytes are emerging as ideal material platform for self-powered bio-compatible electronic devices and sensors. However, despite the nanoscale nature of the ionic thermodiffusion processes underlying thermoelectric efficiency boost in polyelectrolytes, to date no evidence for direct probing of ionic diffusion on its relevant length and time scale has been reported. This gap is bridged by developing heat-driven hybrid nanotransistors based on InAs nanowires embedded in thermally biased Na+ -functionalized (poly)ethyleneoxide, where the semiconducting nanostructure acts as a nanoscale probe sensitive to the local arrangement of the ionic species. The impact of ionic thermoelectric gating on the nanodevice electrical response is addressed, investigating the effect of device architecture, bias configuration and frequency of the heat stimulus, and inferring optimal conditions for the heat-driven nanotransistor operation. Microscopic quantities of the polyelectrolyte such as the ionic diffusion coefficient are extracted from the analysis of hysteretic behaviors rising in the nanodevices. The reported experimental platform enables simultaneously the ionic thermodiffusion and nanoscale resolution, providing a framework for direct estimation of polyelectrolytes microscopic parameters. This may open new routes for heat-driven nanoelectronic applications and boost the rational design of next-generation polymer-based thermoelectricmaterials.

Dual color pH probes made from silica and polystyrene nanoparticles and their performance in cell studies

Ratiometric green–red fluorescent nanosensors for fluorometrically monitoring pH in the acidic range were designed from 80 nm-sized polystyrene (PS) and silica (SiO2) nanoparticles (NPs), red emissive reference dyes, and a green emissive naphthalimide pH probe, analytically and spectroscopically characterized, and compared regarding their sensing performance in aqueous dispersion and in cellular uptake studies. Preparation of these optical probes, which are excitable by 405 nm laser or LED light sources, involved the encapsulation of the pH-inert red-fluorescent dye Nile Red (NR) in the core of self-made carboxylated PSNPs by a simple swelling procedure and the fabrication of rhodamine B (RhB)-stained SiO2-NPs from a silane derivative of pH-insensitive RhB. Subsequently, the custom-made naphthalimide pH probe, that utilizes a protonation-controlled photoinduced electron transfer process, was covalently attached to the carboxylic acid groups at the surface of both types of NPs. Fluorescence microscopy studies with the molecular and nanoscale optical probes and A549 lung cancer cells confirmed the cellular uptake of all probes and their penetration into acidic cell compartments, i.e., the lysosomes, indicated by the switching ON of the green naphthalimide fluorescence. This underlines their suitability for intracellular pH sensing, with the SiO2-based nanosensor revealing the best performance regarding uptake speed and stability.

Nanoscale chemical and structural investigation of solid solution polyelemental transition metal oxide nanoparticles

Although it has been shown that configurational entropy can improve the structural stability in transition metal oxides (TMOs), little is known about the oxidation state of transition metals under random mixing of alloys. Such information is essential in understanding the chemical reactivity and properties of TMOs stabilized by configurational entropy. Herein, utilizing electron energy loss spectroscopy (EELS) technique in an aberration-corrected scanning transmission electron microscope (STEM), we systematically studied the oxidation state of binary (Mn,Fe)3O4, ternary (Mn, Fe, Ni)3O4, and quinary (Mn, Fe, Ni, Cu, Zn)3O4 solid solution polyelemental transition metal oxides (SSP-TMOs) nanoparticles. Our findings show that the random mixing of multiple elements in the form of solid solution phase not only promotes the entropy stabilization but also results in stable oxidation state in transition metals spanning from binary to quinary transition metal oxide nanoparticles.

Nanoscale investigation of surface wettability distribution on bubble nucleation with variable temperature boundary condition

Surface wettability plays an essential role in bubble nucleation. In this article, the molecular dynamics simulation method is conducted to study the bubble nucleation of liquid argon film on a copper substrate with hybrid wettability. Unlike the constant temperature boundary condition, the variable temperature boundary condition is adopted to simulate the bubble nucleation process. The temperature gradually increases from 86 K to 200 K, so the substrate temperature at the bubble nucleation time can be obtained. The potential energy, kinetic energy, total energy, and temperature during bubble nucleation are analyzed. The results show that bubble nucleation occurs when the kinetic energy exceeds the potential energy barrier. A method is used to capture the bubble nucleation process, described from the perspective of total energy. The initial nucleation time of the hybrid wettability surface gradually reduces with the rise of the proportion of the hydrophilic part. Compared with the pure hydrophilic surface, the hybrid wettability surface can achieve faster initial nucleation time and lower nucleation temperature by altering the proportion of wettability. The potential energy and temperature distribution reveal the microscopic mechanism of bubble nucleation. This study provides theoretical guidance for the design of cooling surfaces of micro/nanoelectronic devices.

Tin-bearing magnetite with nanoscale Mg-Si defects: Evidence for the early stages of mineralization in a skarn system

Tin-bearing magnetite is reported from several types of magmatic-hydrothermal ore deposits. The question of whether tin is incorporated within solid solution, as Sn4+, or as nanoinclusions remains open, however. We report a micron- to nanoscale investigation of Sn (Mg, Si)-bearing magnetite from serpentinite in the Dulong Zn-Sn-In skarn, South China, with the dual aims of understanding the mechanisms involved in accommodating Sn and associated elements into the Fe-oxide, and the inferences that this carries for constraining the early stages of skarn formation. Magnetite preserves a range of textures that record the evolution of metasomatism during prograde growth of grain cores and retrograde rim replacement. Observations reveal the presence of chondrodite and sellaite (MgF2) as nanoscale inclusions preserved in magnetite. This implies initiation of the Dulong mineralizing system during a humite-bearing, magnesium skarn stage. Magnesium-Si defects, forming along (110) planes prior to Sn-enrichment, are recognized for the first time. Release of high volatile, F-rich fluids is interpreted to lead to precipitation of cassiterite inclusions along &amp;lt;111*&amp;gt; directions in magnetite.

Current Trends in Nanotheranostics: A Concise Review on Bioimaging and Smart Wearable Technology

The area of interventional nanotheranostics combines the use of interventional procedures with nanotechnology for the detection and treatment of physiological disorders. Using catheters or endoscopes, for example, interventional techniques make use of minimally invasive approaches to diagnose and treat medical disorders. It is feasible to increase the precision of these approaches and potency by integrating nanotechnology. To visualize and target various parts of the body, such as tumors or obstructed blood veins, one can utilize nanoscale probes or therapeutic delivery systems. Interventional nanotheranostics offers targeted, minimally invasive therapies that can reduce side effects and enhance patient outcomes, and it has the potential to alter the way that many medical illnesses are handled. Clinical enrollment and implementation of such laboratory scale theranostics approach in medical practice is promising for the patients where the user can benefit by tracking its physiological state. This review aims to introduce the most recent advancements in the field of clinical imaging and diagnostic techniques as well as newly developed on-body wearable devices to deliver therapeutics and monitor its due alleviation in the biological milieu.

Laboratory experiments based on tip probe － Scanning probe detection and regulation of ferroelectric domains and their microscopic physical properties

&lt;sec&gt;Ferroelectric and multiferroic materials have gained significant attention due to their potential applications in investigating emergent cross-coupling phenomena among spin, charge, orbit, and lattice in correlated electron systems, as well as promising candidates for prospective applications in advanced industries, &lt;i&gt;e.g.&lt;/i&gt; data memory/processing, sensors, actuators, and energy-relevant devices. The structure and dynamic characteristics of ferroelectric domains can significantly affect the physical properties and device functions of materials, such as electrical conductivity, photovoltaics, and magnetoelectric coupling, particularly, novel topological domains can bring many new physical properties. These make it possible to design materials and devices through domain engineering methods. Therefore, exploring the microdomain structures and related physical property is expected to bring new material and device solutions for post-Moore's era information technology.&lt;/sec&gt;&lt;sec&gt;Accurate understanding of domain structures and their corresponding functionalities pose challenges to characterization techniques. In particular, it remains challenging to investigate the dynamics and cross-coupling behaviors on a nanoscale &lt;i&gt;in situ&lt;/i&gt;. Nowadays, it is worthwhile to pay more attention to the multifunctional scanning probe microscopy technique, as it serves as a versatile and powerful nanoscale probe capable of exploring multifunctionalities. Multi-field stimulation such as electric field, magnetic field, light illumination, strain field, and thermal field can be combined with the advanced scanning probe microscopy technique, making it an ideal platform for in-situ manipulation of domain structure and its related functional response on a nano-scale.&lt;/sec&gt;&lt;sec&gt;In this study, we give a brief overview on the recent advances in our research group in detection and manipulation of ferroelectric domains and microscopic physical properties through multifunctional scanning probe microscopy technique. Special attention is paid to those topological domain structures such as vortex, center domain state and bubble domain in size-confined systems (ultrathin films/multilayers and nanodots/nanoislands) and their associated novel physical phenomena. In addition, the controllability of electric field driven magnetic switching in multiferroic heterostructures is also studied through size effect, interfacial coupling and domain engineering. Finally, we present some suggestions for future directions. Most of these studies are conducted by using the tip probe, so it is named the “Laboratory experiments based on tip probe”.&lt;/sec&gt;

Nanoscale Investigation of DNA Demethylation in Leukemia Cells by Means of Ultrasensitive Vibrational Spectroscopy.

DNA methylation is a crucial epigenetic hallmark of cancer development but the experimental methods able to prove nanoscale modifications are very scarce. Over time, Raman and its counterpart, surface-enhanced Raman scattering (SERS), became one of the most promising techniques capable to investigate nanoscale modifications of DNA bases. In our study, we employed Raman/SERS to highlight the differences between normal and leukemia DNA samples and to evaluate the effects of a 5-azacytidine treatment on leukemia cells. To obtain spectral information related to DNA base modifications, a DNA incubation step of 4 min at 94 °C, similar to the one performed in the case of RT-PCR experiments, was conducted prior to any measurements. In this way, reproducible Raman/SERS spectra were collected for all genomic DNA samples. Our Raman results allowed discrimination between normal and cancer DNAs based on their different aggregation behavior induced by the distinct methylation landscape present in the DNA samples. On the other hand, the SERS spectra collected on the same DNA samples show a very intense vibrational band located at 1008 cm-1 assigned to a rocking vibration of 5-methyl-cytosine. The intensity of this band strongly decreases in cancer DNA due to the modification of the methylation landscape occurring in cancers. We believe that under controlled experimental conditions, this vibrational band could be used as a powerful marker for demonstrating epigenetic reprogramming in cancer by means of SERS.

Nanoscale probing of surface potential landscape at MoS2/BP van der Waals p–n heterojunction

2D van der Waals heterostructure paves a path towards next generation semiconductor junctions for nanoelectronics devices in the post silicon era. Probing the band alignment at a real condition of such 2D contacts and experimental determination of its junction parameters is necessary to comprehend the charge diffusion and transport through such 2D nano-junctions. Here, we demonstrate the formation of the p–n junction at the MoS2/Black phosphorene (BP) interface and conduct a nanoscale investigation to experimentally measure the band alignment at real conditions by means of measuring the spatial distribution of built-in potential, built-in electric field, and depletion width using the Kelvin probe force microscopy (KPFM) technique. We show that optimization of lift scan height is critical for defining the depletion region of MoS2/BP with nanoscale precision using the KPFM technique. The variations in the built-in potential and built-in electric field with varying thicknesses of MoS2 are revealed and calibrated.

Biocompatible, Biodegradable, and Improved Fluorescent Silicon Quantum Dots for Zebrafish Imaging

One of the greatest benefits of nanomedicine elucidated to date includes the non-invasive tracking and monitoring of living organisms by the selective uptake of harmless metallic nanoparticles. Several nanoscale probes have been employed for biomolecular imaging. Among them, fluorescent nanoscale silicon materials have been recently established with a strong and safe potential for bioimaging and biosensing applications due to their bright fluorescence coupled with strong photostability, biocompatibility and negligible toxicity. Herein, we developed high-quality silicon nanomaterials (4–5 nm; SiNPs) as biological fluorescent probes for bioimaging of living organisms through an easy aquatic synthesis method with a quantum yield of ∼8%. In this regard, we report that the presently synthesized SiNPs-based sensors/probes are attractive materials for solvent-based fluorescence measurements and are biocompatible, non-toxic, highly photo-stable and pH stable. Most importantly, their fluorescence lifetime is much longer than that of native probes in living cells. Thus, these presently formulated SiNPs are improved fluorescent probes for in vivo biological imaging in zebra fish embryos as well as numerous other living organisms and, thus, should be further studied.