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1.
Anal Chem ; 2020 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-32349475

RESUMO

Hydrocarbon gases especially toxic ones like benzene and xylene pose threats to human health and environment. But existing detection techniques like bulky GC-MS or portable PID cannot fulfill people's requirement of affordable and reliable hydrocarbons monitoring for the purpose of personal exposure assessment. Here, a simple, low cost and light hydrocarbon gases sensor using smartphone camera as readout was developed based on the paper based milli-cantilever bending induced by polymer swelling. Its sensing cantilever was composed of 3 layers: functional layer of polyethylene film, adhesive layer of double-side tape and substrate of weighing paper. And the dimensions of the micro-fabricated sensing cantilever are 8 mm long, 0.5 mm wide and 50 µm thick. The sensor response was the displacement of milli-cantilever free end. As proof of concept, its performance to typical hydrocarbons of xylene, hexane and BTEX was carefully examined. For all of them, the sensor showed good performance of linear response to hydrocarbon concentrations, wide detection range, low detection, and fast response. Taking xylene for example, the sensor showed wide detection range of 15-140 ppm, low detection limit of 15 ppm, and fast response of 30 s. The sensor cross-sensitivity to other hydrocarbons was consistent with polymer swelling theory that the more carbons the hydrocarbon has, the higher the sensor sensitivity. Take advantage of the rough materials chosen and simple fabrication procedure, the developed sensors also had high stability with time, low cost and good uniformity. The developed sensor is affordable both physically and financially, has good performance, could meet hydrocarbons monitoring requirements for occupational safety or air pollution in petroleum industry, and would benefit people health.

2.
ACS Sens ; 5(4): 1126-1131, 2020 04 24.
Artigo em Inglês | MEDLINE | ID: mdl-32180397

RESUMO

A rapid and sensitive method to detect cardiac troponin I (cTnI) in human blood is critical to the diagnosis and treatment of acute myocardial infarction (AMI). Here, we describe a simple one-step digital immunoassay for single-molecule detection without washing steps. A sample containing cTnI mixed with detection antibody-conjugated gold nanoparticles (AuNPs) is added to a capture antibody-coated sensor surface and the formation of the antibody-cTnI-antibody sandwich is detected by digitally counting the binding of the individual gold nanoparticles to the sensor surface in real time using a bright-field optical imaging setup together with a differential imaging algorithm. The digital immunoassay detects cTnI in undiluted human plasma, which achieves a detection limit of 5.7 ng/L within a detection time of only 10 min, which meets the requirement of current clinical high-sensitivity troponin assay (∼70 ng/L cutoff). We anticipate that the one-step and real-time digital immunoassay can be applied to the detection of other disease biomarkers in blood.

3.
Anal Chem ; 92(8): 5904-5909, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32216299

RESUMO

Charge is a fundamental property of a molecule, and precisely measuring it enables detection of the molecule and helps understand various chemical processes involving charge. Here we show a method to measure the charge of a single nanoparticle and binding of charged molecules to the nanoparticle using a conventional bright field optical microscope. The nanoparticle is tethered to an indium tin oxide surface with a polymer and driven into oscillation with an alternating electric field, which produces scattered light captured by a camera. The weak scattered light is separated from the intense bright field background using a Fourier transform filter, and the image contrast change provides the effective charge of the nanoparticle with precision of a few electron charges or less. This method allows us to detect DNA binding to the nanoparticles, demonstrating a simple method to detect and study molecules with a conventional optical microscope.

5.
Anal Chem ; 92(1): 799-805, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31762258

RESUMO

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O2 sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O2 concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO2 sensor linearly responded to NO2 concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.

6.
7.
Anal Chem ; 91(21): 14149-14156, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31593433

RESUMO

Measuring ligand-protein interactions is critical for unveiling molecular-scale biological processes in living systems and for screening drugs. Various detection technologies have been developed, but quantifying the binding kinetics of small molecules to the proteins remains challenging because the sensitivities of the mainstream technologies decrease with the size of the ligand. Here, we report a method to measure and quantify the binding kinetics of both large and small molecules with self-assembled nano-oscillators, each consisting of a nanoparticle tethered to a surface via long polymer molecules. By applying an oscillating electric field normal to the surface, the nanoparticle oscillates, and the oscillation amplitude is proportional to the number of charges on the nano-oscillator. Upon the binding of ligands onto the nano-oscillator, the oscillation amplitude will change. Using a plasmonic imaging approach, the oscillation amplitude is measured with subnanometer precision, allowing us to accurately quantify the binding kinetics of ligands, including small molecules, to their protein receptors. This work demonstrates the capability of nano-oscillators as an useful tool for measuring the binding kinetics of both large and small molecules.

8.
Nat Commun ; 10(1): 4599, 2019 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-31601813

RESUMO

Host-guest interactions are of central importance in many biological and chemical processes. However, the investigation of the formation and decomplexation of host-guest systems at the single-molecule level has been a challenging task. Here we show that the single-molecule conductance of organoplatinum(II) metallocycle hosts can be enhanced by an order of magnitude by the incorporation of a C60 guest molecule. Mechanically stretching the metallocycle-C60 junction with a scanning tunneling microscopy break junction technique causes the release of the C60 guest from the metallocycle, and consequently the conductance switches back to the free-host level. Metallocycle hosts with different shapes and cavity sizes show different degrees of flexibility to accommodate the C60 guest in response to mechanical stretching. DFT calculations provide further insights into the electronic structures and charge transport properties of the molecular junctions based on metallocycles and the metallocycle-C60 complexes.


Assuntos
Fulerenos/química , Compostos Organoplatínicos/química , Teoria da Densidade Funcional , Eletrodos , Ouro , Espectroscopia de Ressonância Magnética , Microscopia de Força Atômica , Microscopia de Tunelamento , Espectrofotometria Ultravioleta
9.
J Am Chem Soc ; 141(40): 16071-16078, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31525042

RESUMO

Measuring binding between molecules is critical for understanding basic biochemical processes, developing molecular diagnosis, and screening drugs. Here we study molecular binding at the single molecule level by attaching nanoparticles to the molecular binding pairs. We track the thermal fluctuations of the individual nanoparticles with sub-nanometer precision using a plasmonic scattering imaging technique and show that the fluctuations are controlled by the molecular binding pairs rather than by the nanoparticles. Analysis of the thermal fluctuations provides unique information on molecular binding, including binding energy profile, effective spring constant, and switching between single and multiple molecular binding events. The method provides new insights into molecular binding and also allows one to differentiate nonspecific binding from specific binding, which has been a difficult task in biosensors.

10.
ACS Sens ; 4(8): 2205-2212, 2019 08 23.
Artigo em Inglês | MEDLINE | ID: mdl-31348853

RESUMO

Exocytosis involves interactions between secretory vesicles and the plasma membrane. Studying the membrane response is thus critical to understand this important cellular process and to differentiate different mediator release patterns. Here we introduce a label-free optical imaging method to detect the vesicle-membrane-interaction-induced membrane deformation associated with single exocytosis in mast cells. We show that the plasma membrane expands by a few tens of nanometers accompanying each vesicle-release event, but the dynamics of the membrane deformation varies from cell to cell, which reflect different exocytosis processes. Combining the temporal and spatial information allows us to resolve complex vesicle-release processes, such as two vesicle-release events that occur closely in time and location. Simultaneous following a vesicle release with fluorescence and membrane deformation tracking further allows us to determine the propagation speed of the vesicle-release-induced membrane deformation along the cell surface, which has an average value of 5.2 ± 1.8 µm/s.

11.
J Am Chem Soc ; 141(29): 11694-11699, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31260624

RESUMO

We study electron transfer associated with electrocatalytic reduction of hydrogen on single platinum nanoparticles separated from an electrode surface with an alkanethiol monolayer using a plasmonic imaging technique. By varying the monolayer thickness, we show that the reaction rate depends on electron tunneling from the electrode to the nanoparticle. The tunneling decay constant is ∼4.3 nm-1, which is small compared to those in literature for alkanethiols. We attribute it to a reduced tunneling barrier resulting from biasing the electrode potential negatively to the hydrogen reduction regime. In addition to allowing study of electron transfer of single nanoparticles, the work demonstrates an optical method to measure charge transport in molecules electrically wired to two electrodes.

12.
ACS Nano ; 13(8): 8609-8617, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31276361

RESUMO

Timely diagnosis of acute diseases improves treatment outcomes and saves lives, but it requires fast and precision quantification of biomarkers. Here, we report a time-resolved digital immunoassay based on plasmonic imaging of binding of single nanoparticles to biomarkers captured on a sensor surface. The real-time and high contrast of plasmonic imaging lead to fast and precise counting of the individual biomarkers over a wide dynamic range. We demonstrated the detection principle, evaluated the performance of the method using procalcitonin (PCT) as an example, and achieved a limit of detection of ∼2.8 pg/mL, dynamic range of 4.2-12500 pg/mL, for a total detection time of ∼25 min.

13.
J Biomed Opt ; 24(6): 1-7, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31222988

RESUMO

A membrane potential change in cells is accompanied with mechanical deformation. This electromechanical response can play a significant role in regulating action potential in neurons and in controlling voltage-gated ion channels. However, measuring this subtle deformation in mammalian cells has been a difficult task. We show a plasmonic imaging method to image mechanical deformation in single cells upon a change in the membrane potential. Using this method, we have studied the electromechanical response in mammalian cells and have observed the local deformation within the cells that are associated with cell-substrate interactions. By analyzing frequency dependence of the response, we have further examined the electromechanical deformation in terms of mechanical properties of cytoplasm and cytoskeleton. We demonstrate a plasmonic imaging approach to quantify the electromechanical responses of single mammalian cells and determine local variability related to cell-substrate interactions.

14.
Anal Chem ; 91(15): 10164-10171, 2019 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-31251566

RESUMO

The emergence of antibiotic resistance has prompted the development of rapid antimicrobial susceptibility testing (AST) technologies that will enable evidence-based treatment and promote antimicrobial stewardship. To date, many rapid AST methods have been developed, but few are able to be performed on clinical samples directly. Here we developed a large volume light scattering microscopy technique that tracks phenotypic features of single bacterial cells directly in clinical urine samples without sample enrichment or culturing. The technique demonstrated rapid (90 min) detection of Escherichia coli in 24 clinical urine samples with 100% sensitivity and 83% specificity and rapid (90 min) AST in 12 urine samples with 87.5% categorical agreement with two antibiotics, ampicillin and ciprofloxacin.

15.
Nat Commun ; 10(1): 1997, 2019 04 30.
Artigo em Inglês | MEDLINE | ID: mdl-31040288

RESUMO

Human G protein-coupled receptors (GPCRs) respond to various ligands and stimuli. However, GPCRs rely on membrane for proper folding, making their biochemical properties difficult to study. By displaying GPCRs in viral envelopes, we fabricated a Virion Display (VirD) array containing 315 non-olfactory human GPCRs for functional characterization. Using this array, we found that 10 of 20 anti-GPCR mAbs were ultra-specific. We further demonstrated that those failed in the mAb assays could recognize their canonical ligands, suggesting proper folding. Next, using two peptide ligands on the VirD-GPCR array, we identified expected interactions and novel interactions. Finally, we screened the array with group B Streptococcus, a major cause of neonatal meningitis, and demonstrated that inhibition of a newly identified target, CysLTR1, reduced bacterial penetration both in vitro and in vivo. We believe that the VirD-GPCR array holds great potential for high-throughput screening for small molecule drugs, affinity reagents, and ligand deorphanization.


Assuntos
Receptores Acoplados a Proteínas-G/metabolismo , Vírion/metabolismo , Animais , Western Blotting , Imunofluorescência , Células HEK293 , Células HeLa , Humanos , Proteômica/métodos , Streptococcus/metabolismo , Células Vero , Virologia/métodos
16.
Anal Chem ; 91(10): 6632-6637, 2019 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-31012302

RESUMO

Colorimetry is a popular gas-sensing platform, but it is typically limited to one-time use only. Here, we introduce a light-controlled configurable colorimetric sensing array to overcome this limitation. It features a photoactivated reaction between an analyte and a sensing material, such that sensing of an array element can be turned on and off with light. By sequential turning on of each array element, the sensor array can be used multiple times as determined by the number of array elements. This is analogous to a data storage device, which lasts until every storage element is used up. The total number of array elements and the area of each array element are configurable with light. With use of a smartphone screen as a programmable light source, we applied the sensing platform to the detection of oxygen gas and studied the relationship between sensitivity, noise, detection time, and array size. The relationship can be used to configure the array to meet the specifications of different applications.

17.
ACS Sens ; 4(4): 780, 2019 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-31023013
18.
Proc Natl Acad Sci U S A ; 116(9): 3407-3412, 2019 02 26.
Artigo em Inglês | MEDLINE | ID: mdl-30737288

RESUMO

Electron transfer reactions can now be followed at the single-molecule level, but the connection between the microscopic and macroscopic data remains to be understood. By monitoring the conductance of a single molecule, we show that the individual electron transfer reaction events are stochastic and manifested as large conductance fluctuations. The fluctuation probability follows first-order kinetics with potential dependent rate constants described by the Butler-Volmer relation. Ensemble averaging of many individual reaction events leads to a deterministic dependence of the conductance on the external electrochemical potential that follows the Nernst equation. This study discloses a systematic transition from stochastic kinetics of individual reaction events to deterministic thermodynamics of ensemble averages and provides insights into electron transfer processes of small systems, consisting of a single molecule or a small number of molecules.

19.
Nat Mater ; 18(4): 357-363, 2019 04.
Artigo em Inglês | MEDLINE | ID: mdl-30742082

RESUMO

Quantum interference can profoundly affect charge transport in single molecules, but experiments can usually measure only the conductance at the Fermi energy. Because, in general, the most pronounced features of the quantum interference are not located at the Fermi energy, it is highly desirable to probe charge transport in a broader energy range. Here, by means of electrochemical gating, we measure the conductance and map the transmission functions of single molecules at and around the Fermi energy, and study signatures associated with constructive and destructive interference. With electrochemical gate control, we tune the quantum interference between the highest occupied molecular orbital and lowest unoccupied molecular orbital, and directly observe anti-resonance, a distinct feature of destructive interference. By tuning the molecule in and out of anti-resonance, we achieve continuous control of the conductance over two orders of magnitude with a subthreshold swing of ~17 mV dec-1, features relevant to high-speed and low-power electronics.

20.
ACS Nano ; 13(2): 2298-2306, 2019 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-30636406

RESUMO

Mapping local surface charge distribution is critical to the understanding of various surface processes and also allows the detection of molecules binding to the surface. We show here that the optical absorption of monolayer MoS2 is highly sensitive to charge and demonstrate optical imaging of local surface charge distribution with this atomically thin material. We validate the imaging principle and perform charge sensitivity calibration with an electrochemical gate. We further show that binding of charged molecules to the atomically thin material leads to a large change in the image contrast, allowing determination of the charge of the adsorbed molecules. This capability opens possibilities for characterizing impurities and defects in two-dimensional materials and for label-free optical detection and charge analysis of molecules.

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