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Nanomaterials ◽  
2022 ◽  
Vol 12 (2) ◽  
pp. 242
Author(s):  
Almudena Marti ◽  
Jurriaan Huskens

Affinity sensing of nucleic acids is among the most investigated areas in biosensing due to the growing importance of DNA diagnostics in healthcare research and clinical applications. Here, we report a simple electrochemical DNA detection layer, based on poly-l-lysine (PLL), in combination with gold nanoparticles (AuNPs) as a signal amplifier. The layer shows excellent reduction of non-specific binding and thereby high contrast between amplified and non-amplified signals with functionalized AuNPs; the relative change in current was 10-fold compared to the non-amplified signal. The present work may provide a general method for the detection of tumor markers based on electrochemical DNA sensing.


2022 ◽  
Author(s):  
Won-Hwa Park

Abstract Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics and bio-sensing. In order to apply graphene in the medical field, chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogenious carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-Enhanced Raman Spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD–grown GM (CVD-GM) by applying a Nanoparticle-on-Mirror (NPoM) system composed of Au nanoparticle (NP) / CVD-GM / Au thin film (TF) plasmonic junction structure. A new (or enhanced) Radial Breathing Like Mode (RBLM) SERS signal around ~150 cm-1 from CVD-GM spaced in NPoM is clearly observed by employing a local z-polarized incident field formed at the Au NP–Au TF plasmonic gap junctions. With this observation, the value of I[out-of-plane, RBLM] / I[in-plane, [2D] at certain domains, it can be suggested as a new optical nano-metrology value to relatively determine between lower z-directional morphological corrugation (or protrusion) status of a CVD-GM spaced in our NPoM system (lower I[RBLM] / I[2D] value) and higher degree of lateral carrier mobility of the CVD-GM associated with lower sheet resistance values as a result of higher blue-shifted Raman in-plane (G, 2D) peak maximum position. Furthermore, we will also expect the bio-sensing performances by utilizing the high specific surface area and ultrahigh flexibility of the CVD-GM in one of the future prospective works such as pressure-strain, strain-to-electricity and chemical-coupled sensor via I[RBLM] / I[2D] values.


RSC Advances ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 193-200
Author(s):  
Gasidit Panomsuwan ◽  
Sittan Wongcharoen ◽  
Chayanapat Chokradcharoen ◽  
Mongkol Tipplook ◽  
Oratai Jongprateep ◽  
...  

Plasmonic Au nanoparticles-decorated TiO2 hollow fibers with enhanced visible-light photocatalytic activity have been successfully prepared by a two-step process: (i) template method using kapok and (ii) solution plasma process.


Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 106
Author(s):  
Xiaoqing Deng ◽  
Yu Ding ◽  
Xiaobing Wang ◽  
Xiaojing Jia ◽  
Shuo Zhang ◽  
...  

The performance of CO oxidation over plasmonic Au/TiO2 photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO2, an O2 and Ar mixture gas as a discharge gas was employed to activate Au/TiO2. The photocatalytic activity in CO oxidation over activated Au/TiO2 was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O2 content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO2 rises rapidly at first and then remains constant at 75% when the O2 content is above 50%. Compared with the discharge gas of 10% and 30% O2/Ar, the sample activated by 50% O2/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO2 is discovered.


2021 ◽  
Vol 14 (1) ◽  
pp. 228
Author(s):  
Xiaoqiao Huang ◽  
Li Cai ◽  
Tingting Fan ◽  
Kexi Sun ◽  
Le Yao ◽  
...  

Here we report a simple fabrication method for large-scale hybrid surface-enhanced Raman scattering (SERS) active substrates composed of Au-nanoparticle-decorated three-dimensional (3D) Cu(OH)2@HKUST-1 (Cu3(btc)2, H3btc = 1,3,5-benzenetricarboxylic acid) nanorod arrays on a woven Cu mesh (Cu mesh/Cu(OH)2@HKUST-1@Au). Cu(OH)2 nanorods were first obtained from a simple in situ chemical engraving Cu mesh and then utilized as self-sacrificing templates to achieve HKUST-1 nanocube-assembled nanorods; finally, Au nanoparticles (Au NPs) were sputtered onto the Cu(OH)2@HKUST-1 nanorods. Due to the large surface area, the three-dimensional Cu mesh/Cu(OH)2@HKUST-1 nanorods could load high-density Au NPs and capture target detection molecules, which is beneficial to the formation of a strong electromagnetic field coupling between Au NPs, and provides abundant “hot spots” for a sensitive and uniform SERS effect. Using the Cu mesh/Cu(OH)2@HKUST-1@Au nanorod arrays as the SERS substrate, 10−9 M Rhodamine 6G and 10−8 M 4-aminothiophenolcan were identified. To verify their practical application, the fabricated arrays were employed as SERS substrates for the detection of thiram, and 10−8 M thiram could be recognized. The hybrid SERS substrates show potential applications in the field of environmental pollutant detection and this is of great significance to the sustainable development of the environment.


Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2256
Author(s):  
Žiga Jelen ◽  
Domen Kandare ◽  
Luka Lešnik ◽  
Rebeka Rudolf

An ultrasonic spray pyrolysis (USP) device consists of an evaporation and two reaction zones of equal length, into which an aerosol with a precursor compound enters, and where nanoparticles are formed in the final stage. As part of this research, we simulated the geometry of a side inlet, where the reaction gas (H2) enters into the reaction tube of the device by using numerical methods. Mixing with the carrier gas (N2) occurs at the entry of the H2. In the initial part, we performed a theoretical calculation with a numerical simulation using ANSYS CFX, while the geometries of the basic and studied models were prepared with Solidworks. The inlet geometry of the H2 included a study of the position and radius of the inlet with respect to the reaction tube of the USP device, as well as a study of the angle and diameter of the inlet. In the simulation, we chose the typical flows of both gases (N2, H2) in the range of 5 L/min to 15 L/min. The results show that the best geometry is with the H2 side inlet at the bottom, which the existing USP device does not allow for. Subsequently, temperature was included in the numerical simulation of the basic geometry with selected gas flows; 150 °C was considered in the evaporation zone and 400 °C was considered in the other two zones—as is the case for Au nanoparticle synthesis. In the final part, we performed an experiment on a USP device by selecting for the input parameters those that, theoretically, were the most appropriate—a constant flow of H2 5 L/min and three different N2 flows (5 L/min, 10 L/min, and 15 L/min). The results of this study show that numerical simulations are a suitable tool for studying the H2 flow in a UPS device, as the obtained results are comparable to the results of experimental tests that showed that an increased flow of N2 can prevent the backflow of H2 effectively, and that a redesign of the inlet geometry is needed to ensure proper mixing. Thus, numerical simulations using the ANSYS CFX package can be used to evaluate the optimal geometry for an H2 side inlet properly, so as to reconstruct the current and improve future USP devices.


2021 ◽  
Author(s):  
◽  
Omar Ahmed Alsager

<p>Aptamers are synthetic nucleic acid single stranded (ss)DNAs or RNAs that can bind with high affinity and specificity to a broad range of targets, including proteins and low molecular weight molecules. This work presents the design, development and implementation of novel aptamer based sensors (aptasensors) for the detection of a target of environmental and medical significance - 17-β estradiol (E2). By combining a previously isolated E2 binding 75-mer ssDNA aptamer with a variety of different signal transducers, E2 was successfully detected and quantified below the environmental and biological relevant concentrations. By applying the same aptamer to different sensor formats, the advantages and disadvantages of each signal transduction mechanism were compared.  Target-induced conformational switch within an aptamer molecule can be transduced via labelling different sections of the aptamer with pairs of fluorescent dyes or with a redox probe, however those strategies require detailed knowledge of specific aptamer conformations and target interaction sites. Herein, a label free method is developed - size based aptasensor described in Chapter 2. The new method only depends on the general property that small molecule binding aptamers adopt a more compact folded structure when they bind to their target. Dynamic light scattering (DLS) and tunable resistive pulse sensing (TRPS) were used to probe recognition events between E2 and aptamers conjugated to carboxylated polystyrene nanoparticles (NPs). Upon E2 recognition, a distinct reduction in size and a less negative surface potential of the conjugated particles were observed, which can be correlated to the concentration of E2 in the lower nanomolar range (as low as 5 nM).  On-site monitoring of E2 requires rapid and sensitive screening methods with minimal instrumentation. Previously, gold nanoparticles (AuNPs) were exploited in the construction of colorimetric aptasensors for different targets. Aggregation assays produce colorimetric signals observed by naked-eye when target-bound aptamers dissociate from AuNP surfaces, triggering aggregation. However, it is unknown how the length of aptamer sequences affects their dissociation from AuNP surfaces and subsequent aggregation. Chapter 3 demonstrates the benefit of editing aptamer sequences with specific regard to the way signals are transduced in AuNP based colorimetric assays. The 20 flanking nucleotides to the 35-mer inner core of the parent 75-mer aptamer were eliminated. The 35-mer aptamer has a lower dissociation constant KD (14 nM vs. 25 nM), improved discrimination against other steroidal molecules and greatly improve the sensitivity for E2 detection from 5 nM to 200 pM. In fact, this simple strategy enabled facile detection of E2 in urine at 5 nM, approaching levels of biological relevance.  There is a pressing demand for methods with accurate and rapid performance to detect and quantify E2, at levels comparable or even below the biological concentrations to eliminate pre-concentration and sample purification process. Existing electrochemical aptasensors feature DNA probes covalently tethered to various surfaces including gold and conducting polymer electrode. An electrochemical impedance spectroscopy (EIS) based sensor was created using nanoporous conducting polymer electrodes functionalized with the 75-mer aptamer. The one fM detection limit found is one order of magnitude lower than the recorded biological level. As a novel alternative approach, sensing electrodes were also created via the non-specific adsorption of the 35-mer onto Au and Au nanoparticle electrodes. This approach, described in Chapter 4, led to the same level of detection as the conducting polymer aptasensor, but via a mechanism with similarities to the colorimetric sensor. Non-specific adsorption of aptamers to Au was found to play additional favourable roles including self-passivation and stabilization of Au nanoparticle based electrodes. Sensing with this format might remove the need for laborious surface passivation with alkylthiol molecules encountered with the conventional covalent attachment of the DNAs through thiol-linkers.  In general, the reported aptasensors provide efficient means to detect the steroidal molecule E2 as well as advance the understanding of aptasensors by comparing the performance of the same aptamer in various sensing platforms. Long aptamers sequences appeared to be more efficient in signal transduction when specific surface tethering is involved, as in the size-based assay, and the electrochemical assay with aptamers covalently tethered to the electrode. Here, the non-binding flanking nucleotides, i.e. nucleotides adjacent to the target binding pocket, appeared to amplify the sensing signals. However, shorter truncated sequences showed better performance when signal generation depends on surface dissociation of non-specifically adsorbed aptamer sequences, as in the colorimetric assay, and the electrochemical sensor constructed from adsorbed aptamers. These insights can be readily applied to aptasensors for the growing range of targets.</p>


2021 ◽  
Author(s):  
◽  
Omar Ahmed Alsager

<p>Aptamers are synthetic nucleic acid single stranded (ss)DNAs or RNAs that can bind with high affinity and specificity to a broad range of targets, including proteins and low molecular weight molecules. This work presents the design, development and implementation of novel aptamer based sensors (aptasensors) for the detection of a target of environmental and medical significance - 17-β estradiol (E2). By combining a previously isolated E2 binding 75-mer ssDNA aptamer with a variety of different signal transducers, E2 was successfully detected and quantified below the environmental and biological relevant concentrations. By applying the same aptamer to different sensor formats, the advantages and disadvantages of each signal transduction mechanism were compared.  Target-induced conformational switch within an aptamer molecule can be transduced via labelling different sections of the aptamer with pairs of fluorescent dyes or with a redox probe, however those strategies require detailed knowledge of specific aptamer conformations and target interaction sites. Herein, a label free method is developed - size based aptasensor described in Chapter 2. The new method only depends on the general property that small molecule binding aptamers adopt a more compact folded structure when they bind to their target. Dynamic light scattering (DLS) and tunable resistive pulse sensing (TRPS) were used to probe recognition events between E2 and aptamers conjugated to carboxylated polystyrene nanoparticles (NPs). Upon E2 recognition, a distinct reduction in size and a less negative surface potential of the conjugated particles were observed, which can be correlated to the concentration of E2 in the lower nanomolar range (as low as 5 nM).  On-site monitoring of E2 requires rapid and sensitive screening methods with minimal instrumentation. Previously, gold nanoparticles (AuNPs) were exploited in the construction of colorimetric aptasensors for different targets. Aggregation assays produce colorimetric signals observed by naked-eye when target-bound aptamers dissociate from AuNP surfaces, triggering aggregation. However, it is unknown how the length of aptamer sequences affects their dissociation from AuNP surfaces and subsequent aggregation. Chapter 3 demonstrates the benefit of editing aptamer sequences with specific regard to the way signals are transduced in AuNP based colorimetric assays. The 20 flanking nucleotides to the 35-mer inner core of the parent 75-mer aptamer were eliminated. The 35-mer aptamer has a lower dissociation constant KD (14 nM vs. 25 nM), improved discrimination against other steroidal molecules and greatly improve the sensitivity for E2 detection from 5 nM to 200 pM. In fact, this simple strategy enabled facile detection of E2 in urine at 5 nM, approaching levels of biological relevance.  There is a pressing demand for methods with accurate and rapid performance to detect and quantify E2, at levels comparable or even below the biological concentrations to eliminate pre-concentration and sample purification process. Existing electrochemical aptasensors feature DNA probes covalently tethered to various surfaces including gold and conducting polymer electrode. An electrochemical impedance spectroscopy (EIS) based sensor was created using nanoporous conducting polymer electrodes functionalized with the 75-mer aptamer. The one fM detection limit found is one order of magnitude lower than the recorded biological level. As a novel alternative approach, sensing electrodes were also created via the non-specific adsorption of the 35-mer onto Au and Au nanoparticle electrodes. This approach, described in Chapter 4, led to the same level of detection as the conducting polymer aptasensor, but via a mechanism with similarities to the colorimetric sensor. Non-specific adsorption of aptamers to Au was found to play additional favourable roles including self-passivation and stabilization of Au nanoparticle based electrodes. Sensing with this format might remove the need for laborious surface passivation with alkylthiol molecules encountered with the conventional covalent attachment of the DNAs through thiol-linkers.  In general, the reported aptasensors provide efficient means to detect the steroidal molecule E2 as well as advance the understanding of aptasensors by comparing the performance of the same aptamer in various sensing platforms. Long aptamers sequences appeared to be more efficient in signal transduction when specific surface tethering is involved, as in the size-based assay, and the electrochemical assay with aptamers covalently tethered to the electrode. Here, the non-binding flanking nucleotides, i.e. nucleotides adjacent to the target binding pocket, appeared to amplify the sensing signals. However, shorter truncated sequences showed better performance when signal generation depends on surface dissociation of non-specifically adsorbed aptamer sequences, as in the colorimetric assay, and the electrochemical sensor constructed from adsorbed aptamers. These insights can be readily applied to aptasensors for the growing range of targets.</p>


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