Label-free single-particle imaging approach for ultra-rapid detection of pathogenic bacteria in clinical samples.

Rapid detection of pathogenic bacteria within a few minutes is the key to control infectious disease. However, rapid detection of pathogenic bacteria in clinical samples is quite a challenging task due to the complex matrix, as well as the low abundance of bacteria in real samples. Herein, we employ a label-free single-particle imaging approach to address this challenge. By tracking the scattering intensity variation of single particles in free solution, the morphological heterogeneity can be well identified with particle size smaller than the diffraction limit, facilitating the morphological identification of single bacteria from a complex matrix in a label-free manner. Furthermore, the manipulation of convection in free solution enables the rapid screening of low-abundance bacteria in a small field of view, which significantly improves the sensitivity of single-particle detection. As a proof of concept demonstration, we are able to differentiate the group B streptococci (GBS)-positive samples within 10 min from vaginal swabs without using any biological reagents. This is the most rapid and low-cost method to the best of our knowledge. We believe that such a single-particle imaging approach will find wider applications in clinical diagnosis and disease control due to its high sensitivity, rapidity, simplicity, and low cost.

Absorption-Based Rapid Acquisition of Single-Molecule Kinetics from Unstable Enzymes in Microdroplets.

Single-molecule catalysis reflects the heterogeneity of each molecule, providing a unique insight into the complex catalytic mechanism through the statistics of stochastic individuals. However, the present study methods for single-molecule catalysis are either complicated or have low throughput, limiting their rapid acquisition of single-molecule reaction kinetics with statistical significance. Here, a label-free imaging method is developed for the study of single-molecule catalysis in microdroplets with high throughput based on the absorption of the reaction molecules. A wide distribution of the catalytic reaction rate constant value of 238-2026 molecules s-1 is observed from 68 single enzymes. Interestingly, an exponential decayed distribution of the enzyme activity can be clearly observed due to the rapid denaturation of the enzymes. The denaturation mechanism of the Horse Radish Peroxidase (HRP) enzyme is clarified. It is revealed that the denaturation of each enzyme goes through a gradual decay rather than a truncated turn-off process from a single molecule point of view. This absorption-based method can be applied to most of the catalytic reactions with high throughput, which offers an indispensable route for the rapid statistical analysis of various single-molecule catalytic reactions, making it particularly suitable for the acquisition of catalytic kinetics from highly unstable enzymes.

Comparison of postoperative survival between early-onset and late-onset adenocarcinoma of esophagogastric junction: a population-based study.

BACKGROUND AND AIM: The prognosis of early-onset adenocarcinoma of esophagogastric junction (AEG) remains unclear. This research aimed at comparing the prognosis between early-onset and late-onset AEGs. METHODS: We extracted eligible patients with surgically resected, pathologically confirmed, nonmetastatic AEG from the Surveillance, Epidemiology, and End Results database from 2004 to 2015. The cutoff age of early-onset AEG was set at ≤50 years old. Univariate and multivariate Cox analysis as well as competing risk model were adopted for comparing overall survival (OS) and cancer-specific survival (CSS) between early-onset and late-onset AEGs. In addition, multiple imputation and propensity score matching (PSM) were also carried out for sensitivity analysis. RESULTS: In total, 4610 eligible AEG patients were collected in this study, including 610 early-onset AEGs and 4000 late-onset AEGs. Kaplan-Meier curves revealed significantly better survival in early-onset AEGs than late-onset AEGs. After interpolating missing data by multiple imputation, multivariate Cox regression analysis similarly showed better OS and CSS in early-onset AEGs. By using PSM analysis at a ratio of 1:1, we matched 610 early-onset AEG patients with 610 late-onset AEG patients. After PSM, univariate Cox regression model still revealed favorable prognosis in early-onset AEGs. Similar results were confirmed by performing PSM analysis at a ratio of 1:2 and 1:3. In addition, competing risk model demonstrated significantly lower cancer-specific death in early-onset AEGs compared to late-onset AEGs before and after matching. CONCLUSION: By applying several effective sensitivity analyses, we reported significantly favorable OS and CSS in early-onset AEGs compared to late-onset AEGs.

Photo-Switchable Peroxidase/Catalase-Like Activity of Carbon Quantum Dots.

Nanozymes possess multi-enzyme activities over the natural enzymes, which produce multi-pathway synergistic effects for varies of biomedical applications. Unfortunately, their multi-enzyme activities are in fighting, significantly reducing the synergistic effects. Dynamic regulation of their multi-enzyme activities is the bottleneck for intelligent therapies. Herein, we construct a novel oxygen-nitrogen functionalized carbon quantum dots (O/N-CQDs) with peroxidase-like (Reactive oxygen species (ROS) producer) activity. Interestingly, the peroxidase-like activity can be reversibly converted to catalase-like (ROS scavenger) activity under visible light irradiation. It is found that both the peroxidase/catalase-like activity of O/N-CQDs can be precisely manipulated by the light intensity. The mechanism of switchable enzyme activities is attributed to the polarization of quinoid nitrogen in polyaniline (PANI) precursor retained on O/N-CQDs under visible light, which consumes the ROS to produce O2 and H2O. As a proof-of-concept demonstration, we are able to non-intrusively up and down regulate the ROS level in cells successfully by simply switching off and on the light respectively, potentially facilitating the precise medicine based on the development of the disease. Indeed, the photo-switchable peroxidase/catalase-like activity of O/N-CQDs opens a non-invasive strategy for better manipulations of the multi-activity of nanozymes, promising their wider and more intelligent biomedical applications.

Transient early life growth hormone exposure permanently alters brain, muscle, liver, macrophage, and adipocyte status in long-lived Ames dwarf mice.

The exceptional longevity of Ames dwarf (DF) mice can be abrogated by a brief course of growth hormone (GH) injections started at 2 weeks of age. This transient GH exposure also prevents the increase in cellular stress resistance and decline in hypothalamic inflammation characteristic of DF mice. Here, we show that transient early-life GH treatment leads to permanent alteration of pertinent changes in adipocytes, fat-associated macrophages, liver, muscle, and brain that are seen in DF mice. Ames DF mice, like Snell dwarf and GHRKO mice, show elevation of glycosylphosphatidylinositol specific phospholipase D1 in liver, neurogenesis in brain as indicated by BDNF and DCX proteins, muscle production of fibronectin type III domain-containing protein 5 (a precursor of irisin), uncoupling protein 1 as an index of thermogenic capacity in brown and white fat, and increase in fat-associated anti-inflammatory macrophages. In each case, transient exposure to GH early in life reverts the DF mice to the levels of each protein seen in littermate control animals, in animals evaluated at 15-18 months of age. Thus, many of the traits seen in long-lived mutant mice, pertinent to age-related changes in inflammation, neurogenesis, and metabolic control, are permanently set by early-life GH levels.

Long-term risk of colorectal cancer after removal of adenomas during screening colonoscopies in a large community-based population in China.

Patients with conventional adenoma removal are recommended to undergo colonoscopy surveillance to prevent colorectal cancer (CRC). However, evidence supporting the guidelines of colonoscopy surveillance is limited, especially among the Chinese population. We investigated the association between colonoscopy adenoma findings and CRC risk among individuals aged 40 to 74 years who underwent baseline colonoscopy from 2007 to 2016 in Jiashan and Haining, Zhejiang, China; 34 382 participants were categorized into advanced adenoma, nonadvanced adenoma and no adenoma based on adenoma findings. A multivariable Cox regression model was used to estimate the hazard ratio (HR) of CRC incidence with adjustment for potential confounding factors. After a median follow-up time of 7.7 years, 113 incident cases of CRC were identified (18 occurred in 1632 participants with advanced adenoma, 16 in 3973 participants with nonadvanced adenoma and 79 in 28 777 participants with no adenoma). Compared to no adenoma group, the adjusted HR for CRC in advanced adenoma group was 4.01 (95% CI, 2.37-6.77). For nonadvanced adenomas, individuals with ≥3 adenomas showed an increased risk of CRC (HR, 3.65; 95% CI, 1.43-9.31), but no significantly increased risk of CRC was found for 1 to 2 nonadvanced adenomas, compared to those with no adenoma. Our study suggested that the risk of subsequent CRC increased in individuals with high-risk adenoma (at least one advanced adenoma or ≥3 nonadvanced adenomas), but not in those with 1 to 2 nonadvanced adenomas. These results provide the first evidence from the Chinese population for the current surveillance guidelines.

Fast and Ultrasensitive Visual Detection of Exosomes in Body Fluids for Point-of-Care Disease Diagnosis.

Fast detection of low-concentration exosomes in body fluids is of great significance in understanding the pathogenesis and disease diagnosis but is quite a challenging work due to the complex matrix, tedious pretreatment, and relatively poor sensitivity without the aid of instruments. In this work, by simply using a filter membrane to enrich the exosomes at low concentrations and the use of CuS nanoparticles as labels, we were able to detect exosomes at concentrations as low as 2 × 103 particles/µL in a complex matrix by the naked eye. Due to its high sensitivity, specificity, and simplicity, it can be used for the diagnosis of direct prostate cancer via a 5 mL urine sample within 2 h without the use of any instrument. This method can also be applicable for the detection of other biological nanoparticles, such as viruses, at low concentrations in a complex matrix, offering a promising candidate for point-of-care disease diagnosis with low cost.

Effects of rapamycin on growth hormone receptor knockout mice.

It is well documented that inhibition of mTORC1 (defined by Raptor), a complex of mechanistic target of rapamycin (mTOR), extends life span, but less is known about the mechanisms by which mTORC2 (defined by Rictor) impacts longevity. Here, rapamycin (an inhibitor of mTOR) was used in GHR-KO (growth hormone receptor knockout) mice, which have suppressed mTORC1 and up-regulated mTORC2 signaling, to determine the effect of concurrently decreased mTORC1 and mTORC2 signaling on life span. We found that rapamycin extended life span in control normal (N) mice, whereas it had the opposite effect in GHR-KO mice. In the rapamycin-treated GHR-KO mice, mTORC2 signaling was reduced without further inhibition of mTORC1 in the liver, muscle, and s.c. fat. Glucose and lipid homeostasis were impaired, and old GHR-KO mice treated with rapamycin lost functional immune cells and had increased inflammation. In GHR-KO MEF cells, knockdown of Rictor, but not Raptor, decreased mTORC2 signaling. We conclude that drastic reduction of mTORC2 plays important roles in impaired longevity in GHR-KO mice via disruption of whole-body homeostasis.

Intermittent photocatalytic activity of single CdS nanoparticles.

Semiconductor photocatalysis holds promising keys to address various energy and environmental challenges. Most studies to date are based on ensemble analysis, which may mask critical photocatalytic kinetics in single nanocatalysts. Here we report a study of imaging photocatalytic hydrogen production of single CdS nanoparticles with a plasmonic microscopy in an in operando manner. Surprisingly, we find that the photocatalytic reaction switches on and off stochastically despite the fact that the illumination is kept constant. The on and off states follow truncated and full-scale power-law distributions in broad time scales spanning 3-4 orders of magnitude, respectively, which can be described with a statistical model involving stochastic reactions rates at multiple active sites. This phenomenon is analogous to fluorescence photoblinking, but the underlying mechanism is different. As individual nanocatalyst represents the elementary photocatalytic platform, the discovery of the intermittent nature of the photocatalysis provides insights into the fundamental photochemistry and photophysics of semiconductor nanomaterials, which is anticipated to substantially benefit broad application fields such as clean energy, pollution treatment, and chemical synthesis.

Diet-induced insulin resistance elevates hippocampal glutamate as well as VGLUT1 and GFAP expression in AßPP/PS1 mice.

The symptomologies of Alzheimer's disease (AD) develop over decades suggesting modifiable lifestyle factors may contribute to disease pathogenesis. In humans, hyperinsulinemia associated with type 2 diabetes mellitus increases the risk for developing AD and both diseases share similar age-related etiologies including amyloidogenesis. Since we have demonstrated that soluble Aß42 elicits glutamate release, we wanted to understand how diet-induced insulin resistance alters hippocampal glutamate dynamics, which are important for memory formation and consolidation. Eight to twelve-week-old C57BL/6J and AßPP/PS1 mice were placed on either a low-fat diet or high-fat diet (HFD) for 8 months. A HFD led to significant weight increases as well as impaired insulin sensitivity, glucose tolerance, and learning in both C57BL/6J and AßPP/PS1 mice. AßPP/PS1 low-fat diet mice had elevated hippocampal basal as well as stimulus-evoked glutamate release that was further increased with consumption of a HFD. Immunohistochemistry indicated an increase in vesicular glutamate transporter 1 and glial fibrillary acidic protein density in hippocampal subregions corresponding with this elevated extracellular glutamate. While no differences in hippocampal plaque load were observed, the elevated astrogliotic response surrounding the plaques in AßPP/PS1 HFD mice may have been a compensatory mechanism to control plaque accumulation. These data support that AßPP/PS1 mice have chronically elevated extracellular glutamate that is exacerbated by a HFD and that modifiable lifestyle factors such as obesity-induced insulin resistance can contribute to AD pathogenesis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and for *Open Data* because it made the data publicly available. The data can be accessed at https://osf.io/5whvu (figures for data) and https://osf.io/gd5vf (materials and methods). The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14490.

Self-Reference Analysis Based on Temperature Difference Absorption Spectra.

The direct qualitative identification of pure liquids in laboratories and in security checks is generally performed by the detection of the refractive index or the permittivity. However, refractive indices are strongly influenced by temperature, while the permittivities of some organics are difficult to differentiate. On the other hand, the quantitative monitoring of samples with high concentration in plating baths and in chemical production lines are generally performed via a "Sampling-Dilution-Analysis" approach because of significant deviations from the linear range at high concentration, which makes the real-time monitoring of concentrated samples difficult. Here, we propose a self-reference analysis (SRA) method to directly analyze pure liquids and concentrated samples based on temperature difference absorption spectra (TDAS) without the need for dilution. This method was performed by simultaneously scanning the spectra of the reference and the sample, which are both obtained from the same analyte for detection but are at different temperatures. Compared to conventional absorption spectra with a blank reference, the red-shifted peak wavelengths of TDAS enable the detection of many far UV absorptive compounds in the near-ultraviolet region (λ > 190 nm). More importantly, organic compounds with similar structures can be easily distinguished. In addition, TDAS can also be used for the quantitative detection of concentrated analytes. The proposed SRA-TDAS method is a rapid and effective method; this approach does not require dilution and utilizes a self-reference, implying the wide potential applicability in security checks, and the real-time monitoring of concentrated compounds in chemical production lines.

Intracisternal tuberculoma: a refractory type of tuberculoma indicating surgical intervention.

BACKGROUND: Central nervous system (CNS) tuberculoma is a rare disease with severe neurological deficits. This retrospective research is to review the data of patients diagnosed as CNS tuberculoma. Surgeries were performed in all patients. The clinical features especially the neurological image and the anatomical characters of the tuberculomas were concerned. METHODS: Totally 11 patients diagnosed as CNS tuberculoma were admitted in Guangzhou First People's Hospital (7cases) and Changzheng Hospital (4 cases) during 2006-2015. The data including preoperative condition, neurological imaging, and surgical findings was collected and analyzed. RESULTS: The lesions of nine patients (9/11) were totally or subtotally excised and two (2/11) were partially excised. Neurological functions of all patients were improved after surgery without secondary infection. Lesions of nine (9/11) patients preoperatively progressed as a result of paradoxical reaction. Of the 9 patients demonstrated paradoxical progression, all lesions were partially or totally located at the cisterns or the subarachnoid space. Preoperative ATTs lasted 2 to 12 months and tuberculomas were not eliminated. The arachnoid was found thickened and tightly adhered to the lesions during surgeries. Of the 2 cases that paradoxical reaction were excluded, both patients (case 6, intramedullary tuberculoma; case 11, intradural extramedullary tuberculoma) were admitted at onset of the disease. ATTs were preoperatively given for 1 week as neurological deficits aggravated. The tuberculous lesions of CNS or other system showed no obvious change and paradoxical reaction could not be established in both cases. CONCLUSIONS: Exudates of tuberculosis is usually accumulated in the cisterns and frequently results in the paradoxical formation of tuberculoma. Intracisternal tuberculoma is closely related to paradoxical reaction and refractory to anti-tuberculosis therapy. Micro-surgical excision is safe and effective. Early surgical intervention may be considered in the diagnosis of intracisternal tuberculoma especially when paradoxical reaction participates in the development of tuberculoma.

Optical Imaging of Phase Transition and Li-Ion Diffusion Kinetics of Single LiCoO(2) Nanoparticles During Electrochemical Cycling.

Understanding the phase transition and Li-ion diffusion kinetics of Li-ion storage nanomaterials holds promising keys to further improve the cycle life and charge rate of the Li-ion battery. Traditional electrochemical studies were often based on a bulk electrode consisting of billions of electroactive nanoparticles, which washed out the intrinsic heterogeneity among individuals. Here, we employ optical microscopy, termed surface plasmon resonance microscopy (SPRM), to image electrochemical current of single LiCoO2 nanoparticles down to 50 fA during electrochemical cycling, from which the phase transition and Li-ion diffusion kinetics can be quantitatively resolved in a single nanoparticle, in operando and high throughput manner. SPRM maps the refractive index (RI) of single LiCoO2 nanoparticles, which significantly decreases with the gradual extraction of Li-ions, enabling the optical read-out of single nanoparticle electrochemistry. Further scanning electron microscopy characterization of the same batch of nanoparticles led to a bottom-up strategy for studying the structure-activity relationship. As RI is an intrinsic property of any material, the present approach is anticipated to be applicable for versatile kinds of anode and cathode materials, and to facilitate the rational design and optimization toward durable and fast-charging electrode materials.

Plasmonic Imaging of Electrochemical Reactions of Single Nanoparticles.

Electrochemical reactions are involved in many natural phenomena, and are responsible for various applications, including energy conversion and storage, material processing and protection, and chemical detection and analysis. An electrochemical reaction is accompanied by electron transfer between a chemical species and an electrode. For this reason, it has been studied by measuring current, charge, or related electrical quantities. This approach has led to the development of various electrochemical methods, which have played an essential role in the understanding and applications of electrochemistry. While powerful, most of the traditional methods lack spatial and temporal resolutions desired for studying heterogeneous electrochemical reactions on electrode surfaces and in nanoscale materials. To overcome the limitations, scanning probe microscopes have been invented to map local electrochemical reactions with nanometer resolution. Examples include the scanning electrochemical microscope and scanning electrochemical cell microscope, which directly image local electrochemical reaction current using a scanning electrode or pipet. The use of a scanning probe in these microscopes provides high spatial resolution, but at the expense of temporal resolution and throughput. This Account discusses an alternative approach to study electrochemical reactions. Instead of measuring electron transfer electrically, it detects the accompanying changes in the reactant and product concentrations on the electrode surface optically via surface plasmon resonance (SPR). SPR is highly surface sensitive, and it provides quantitative information on the surface concentrations of reactants and products vs time and electrode potential, from which local reaction kinetics can be analyzed and quantified. The plasmonic approach allows imaging of local electrochemical reactions with high temporal resolution and sensitivity, making it attractive for studying electrochemical reactions in biological systems and nanoscale materials with high throughput. The plasmonic approach has two imaging modes: electrochemical current imaging and interfacial impedance imaging. The former images local electrochemical current associated with electrochemical reactions (faradic current), and the latter maps local interfacial impedance, including nonfaradic contributions (e.g., double layer charging). The plasmonic imaging technique can perform voltammetry (cyclic or square wave) in an analogous manner to the traditional electrochemical methods. It can also be integrated with bright field, dark field, and fluorescence imaging capabilities in one optical setup to provide additional capabilities. To date the plasmonic imaging technique has found various applications, including mapping of heterogeneous surface reactions, analysis of trace substances, detection of catalytic reactions, and measurement of graphene quantum capacitance. The plasmonic and other emerging optical imaging techniques (e.g., dark field and fluorescence microscopy), together with the scanning probe-based electrochemical imaging and single nanoparticle analysis techniques, provide new capabilities for one to study single nanoparticle electrochemistry with unprecedented spatial and temporal resolutions. In this Account, we focus on imaging of electrochemical reactions at single nanoparticles.

Plasmonic Imaging of the Interfacial Potential Distribution on Bipolar Electrodes.

Bipolar electrochemistry is based on the gradient distribution of free-electron density along an electrically isolated electrode, which causes a positive electrode potential at one end and a negative potential at the other, allowing for wide applications in analytical chemistry and materials science. To take full advantage of its wireless and high-throughput features, various types of optical probes, such as pH indicators and fluorescence and electrochemiluminescence reagents, have often been used to indirectly monitor the interfacial electron transfer through chromogenic or fluorogenic reactions. Herein, we report the first probe-free imaging approach that can directly visualize the distribution of the interfacial potential in bipolar electrodes, providing essential information for the validation and development of the theory and applications of bipolar electrochemistry. This approach is based on the sensitive dependence of surface plasmon resonance imaging on the local electron density in the electrode, which enables the direct mapping of potential with a spatial resolution close to the optical diffraction limit, a temporal resolution of 50 ms, and a sensitivity of 10 mV. In addition, in contrast to previous optical readouts that relied on faradaic reactions, the present work achieved the impedance-based measurements under non-faradaic conditions. It is anticipated that this technique will greatly expand the application of bipolar electrochemistry as a platform for chemical and biosensing.

Digitizing Gold Nanoparticle-Based Colorimetric Assay by Imaging and Counting Single Nanoparticles.

Gold colloid changes its color when the internanoparticle distance changes. On the basis of analyte-induced aggregation or disaggregation behavior of gold nanoparticles (AuNPs), versatile colorimetric assays have been developed for measuring various kinds of analytes including proteins, DNA, small molecules, and ions. Traditional read-out signals, which are usually measured by a spectrometer or naked eyes, are based on the averaged extinction properties of a bulk solution containing billions of nanoparticles. Averaged extinction property of a large amount of nanoparticles diminished the contribution from rare events when the analyte concentration was low, thus resulting in limited detection sensitivity. Instead of measuring the averaged optical property from bulk colloid, in the present work, we proposed a digital counterpart of the colorimetric assay by imaging and counting individual AuNPs. This method quantified the analyte concentration with the number percentage of large-sized AuNPs aggregates, which were digitally counted with surface plasmon resonance microscopy (SPRM), a plasmonic imaging technique recently developed by us and other groups. SPRM was able to identify rare AuNPs aggregates despite their small population and greatly improved the detection sensitivity as demonstrated by two model systems based on analyte-induced aggregation and disaggregation, respectively. Furthermore, besides plasmonic AuNPs, SPRM is also suitable for imaging and counting nonplasmonic nanomaterials such as silica and metal oxide with poor extinction properties. It is thus anticipated that the present digitized assay holds a great potential for expanding the colorimetric assay to broad categories of nonplasmonic nanoparticles.

XPLN is an endogenous inhibitor of mTORC2.

Mammalian target of rapamycin complex 2 (mTORC2) controls a wide range of cellular and developmental processes, but its regulation remains incompletely understood. Through a yeast two-hybrid screen, we have identified XPLN (exchange factor found in platelets, leukemic, and neuronal tissues), a guanine nucleotide exchange factor (GEF) for Rho GTPases, as an interacting partner of mTOR. In mammalian cells, XPLN interacts with mTORC2 but not with mTORC1, and this interaction is dependent on rictor. Knockdown of XPLN enhances phosphorylation of the Ser/Thr kinase Akt, a target of mTORC2, whereas overexpression of XPLN suppresses it, suggesting that XPLN inhibits mTORC2 signaling to Akt. Consistent with Akt promoting cell survival and XPLN playing a negative role in this process, XPLN knockdown protects cells from starvation-induced apoptosis. Importantly, this effect of XPLN depletion is abolished by inhibition of Akt or mTOR kinase activity, as well as by rictor knockdown. In vitro, purified XPLN inhibits mTORC2 kinase activity toward Akt without affecting mTORC1 activity. Interestingly, the GEF activity of XPLN is dispensable for its regulation of mTORC2 and Akt in cells and in vitro, whereas an N-terminal 125-amino-acid fragment of XPLN is both necessary and sufficient for the inhibition of mTORC2. Finally, as a muscle-enriched protein, XPLN negatively regulates myoblast differentiation by suppressing mTORC2 and Akt, and this function is through the XPLN N terminus and independent of GEF activity. Our study identifies XPLN as an endogenous inhibitor of mTORC2 and delineates a noncanonical mechanism of XPLN action.

Detection of charges and molecules with self-assembled nano-oscillators.

Detection of a single or small amount of charges and molecules in biologically relevant aqueous solutions is a long-standing goal in analytical science and detection technology. Here we report on self-assembled nano-oscillators for charge and molecular binding detections in aqueous solutions. Each nano-oscillator consists of a nanoparticle linked to a solid surface via a molecular tether. By applying an oscillating electric field normal to the surface, the nanoparticles oscillate, which is detected individually with ∼0.1 nm accuracy by a plasmonic imaging technique. From the oscillation amplitude and phase, the charge of the nanoparticles is determined with a detection limit of ∼0.18 electron charges along with the charge polarity. We further demonstrate the detection of molecular binding with the self-assembled nano-oscillators.

Real-time monitoring of phosphorylation kinetics with self-assembled nano-oscillators.

Phosphorylation is a post-translational modification that is involved in many basic cellular processes and diseases, but is difficult to detect in real time with existing technologies. A label-free detection of phosphorylation is reported in real time with self-assembled nano-oscillators. Each nano-oscillator consists of a gold nanoparticle tethered to a gold surface with a molecular linker. When the nanoparticle is charged, the nano-oscillator can be driven into oscillation with an electric field and detected with a plasmonic imaging approach. The nano-oscillators measure charge change associated with phosphorylation of peptides attached onto a single nanoparticle, allowing us to study the dynamic process of phosphorylation in real time without antibodies down to a few molecules, from which Michaelis and catalytic rate constants are determined.

Plasmonic imaging of electrochemical oxidation of single nanoparticles.

Measuring electrochemical activities of nanomaterials is critical for creating novel catalysts, for developing ultrasensitive sensors, and for understanding fundamental nanoelectrochemistry. However, traditional electrochemical methods measure a large number of nanoparticles, which wash out the properties of individual nanoparticles. We report here a study of transient electrochemical oxidation of single Ag nanoparticles during collision with an electrode and voltammetry of single nanoparticles immobilized on the electrode using a plasmonic-based electrochemical current microscopy. This technique images both electrochemical reaction and size of the same individual nanoparticle, enabling quantitative examination of size-dependent electrochemical activities at single nanoparticle level. The imaging capability further allows detection of the reaction kinetics of each individual nanoparticle and analysis of the average behaviors of multiple nanoparticles. The average kinetics and size dependence can be accurately described by the Tafel equation, but there is a large variability between different nanoparticles, which underscores the importance of single nanoparticle analysis.