We will present surface enhanced Raman spectroscopy (SERS) detection of molecules using plasmonic nanoparticles that are embedded in agarose gel and in filter paper-integrated microfluidic channels, respectively. It has been known that, when SERS detection is performed in complex fluids such as cell culture media, a method to reduce interferences from a variety of molecules in the fluids on the detection results is very important. If continuous monitoring of molecules in cell culture media is needed, there should be a method to prevent large molecules such as proteins from reaching SERS substrates when sample solutions flow over the substrates. Since both agarose gel and filter paper can be used to separate molecules by size, in this study we have integrated them with plasmonic nanoparticles for SERS detection in complex fluids. We will report how to use filter paper-integrated microfluidic channels to detect melamine and sodium thiocyanate (NaSCN) in milk using SERS. In addition, we will demonstrate how to use plasmonic agarose gels to detect illegal drug in urine.
We will present surface enhanced Raman spectroscopy (SERS) and localized surface plasmon resonance (LSPR) detection of hydrogen peroxide (H2O2) using plasmonic gels. It has been known that reactive oxygen species (ROS), such as hydrogen peroxide, are involved in various biological processes, including metabolism, cell signaling, protein folding, biosynthesis, and host defense. Therefore, developing a simple and sensitive method for monitoring ROS levels is very important for live cell studies. Nevertheless, a challenge of utilizing SERS-based or LSPR-based method for molecular detection in complex fluids, such as cell culture media, is that a variety of molecules in sample solutions could interfere with detection results. In addition, when using SERS-based methods, the chance of having the target molecules at the SERS hot spots is reduced when other molecules are present in the solution. To enable detection of H2O2 in cell culture media, we have developed SERS and LSPR detection methods based on gels containing plasmonic nanoparticles. Since gels are filter-like materials, H2O2 can penetrate through the gels, but cells and large molecules such as proteins are blocked. We have successfully utilized these two methods to detect H2O2 in cell culture media without any sample pretreatment.
Localized surface plasmon resonance (LSPR) biosensors have drawn much attention for their promising application in point-of-care diagnostics. While surface plasmon resonance (SPR) biosensing systems have been well developed, LSPR systems have the advantages of simpler and more compact setups. The LSPR peak shifts caused by the binding of molecules to the LSPR substrates, however, are usually smaller than 1 nm if no signal amplification mechanism is used. When using nanoparticles to enhance the sensitivity of LSPR biosensors, because of the short field penetration depth, the nanoparticles should be very close to the LSPR substrate to induce significant shifts in the LSPR peak position. In this study, we used DNA aptamers and gold nanorods to significantly increase the change in the LSPR peak position with the concentration of the target molecules. We have successfully used the proposed mechanism to detect 0.1 nM interferongamma (IFN-γ), a biomarker related to the diagnosis of latent tuberculosis infection. The calibration curves obtained in pure buffers and serum-containing buffers show that accurate detection can be achieved even when the sample is from complex biological fluids such as serum. Because of the enhancement in the sensitivity by the proposed sensing scheme, it is possible to use a low-cost spectrometer to build a LSPR biosensing system.
Surface enhancement Raman spectroscopy (SERS) has drawn much attention in recent years because its ability to greatly enhance Raman signals to allow for the detection of molecules at low concentration. When using metallic nanoparticles as SERS substrates, many studies have shown that the size of the interparticle gap significantly affects the enhancement of the Raman signals. Given that the optimal interparticle gap is as small as a few nanometers, fabricating sensitive, uniform, and reproducible SERS substrates remains challenging. Here we report a three-dimensional SERS substrate created through the assembly of core-shell nanoparticles using DNA. By using DNA of appropriate sequence and length, DNA-functionalized nanoparticles were assembled into ordered and highly packed nanostructures. The interparticle distance was precisely controlled by adjusting the design of the DNA and the thickness of the silver shell coated on the gold nanoparticles. Compared with randomly aggregated nanoparticles, the interparticle distance in the synthesized nanostructures can be more uniform and better controlled. In addition, the DNA-guided assembly process allows us to create precise nanostructures without using complex and expensive fabrication methods. The study demonstrates that the synthesized nanostructures can be used as effective SERS substrates to successfully measure the Raman signals of malachite green, a toxic compound that is sometimes illegally used on fish, as well as Fluorescein isothiocyanate (FITC) at low concentrations.
The study utilized thermophoresis, the directed motion of molecules in a temperature gradient to quantify DNA and
proteins for point-of-care applications. Because the direction and speed of thermophoretic motion is dependent on the size,
charge, and conformation of the molecules, the binding between molecules can induce changes in their thermophoretic
motion. To quantify biomolecules using thermophoresis, we mixed fluorescently-labeled capture probes with samples and
then used an infrared laser to create a temperature gradient in the solution. By adding a small fraction of polymers to the
buffer solution, we accumulated the fluorescent probes in a temperature gradient using the thermophoretic effects. The
thermophoretic motion of the fluorescent probes significantly changed as the target molecules bind to the specially
designed capture probes. Consequently, the level of the thermophoretic accumulation, which was determined by the spatial
distribution of fluorescent probes, could be used to quantify molecules. This method functioned well even when the buffer
contained 10% serum, which suggested that the detection was resistant to the interferences from the molecules in serum.
The thermophoresis-based detection method developed in this study only requires a laser and an epi-fluorescence
microscope during the detection. Unlike many other commonly seen biosensing methods, quantifying molecules using
thermophoresis does not need any fluid channels or pumps for washing away unbound molecules during the detection
process. In addition, the detection does not rely on any micro- or nanofabricated chips. In short, this thermophoresis-based
biosensing method can be a simple, robust, and sensitive method for quantifying proteins and DNA.
We have used constant force axial optical tweezers to understand the subtle eects of sequence variations on the
mechanical properties of DNA. Using designed sequences of DNA with nearly identical curvatures, but varied AT
content, we have shown the persistence length to be highly dependent on the elasticity of DNA. The persistence
length varies by almost thirty percent between sequences containing 61% AT and 45% AT. The biological
implications of this can be substantial, as the need to bend DNA is involved in a host of regulatory schemes,
ranging from nucleosome positioning to the formation of protein-mediated repressor and enhancer loops.
Forces on the order of a hundred femtonewtons can drastically prevent the formation of protein-mediated DNA loops,
which are a common regulatory component of cellular function and control. To investigate how such an acutely sensitive
mechanism might operate within a noisy environment, as might typically be experienced within a cell, we have studied
the response of DNA loop formation under an optically induced, fluctuating, mechanical tension. We show that
mechanical noise strongly enhances the rate of loop formation. Moreover, the sensitivity of the loop formation rate to
mechanical fluctuations is relatively independent of the baseline tension. This suggests that tension along the DNA
molecule could act as a robust means of regulating transcription in a noisy in vivo environment.
We have measured the entropic elasticity of ds-DNA molecules ranging from 247 to 1298 base pairs in length, using
axial optical force-clamp tweezers. We show that entropic end effects and excluded-volume forces become significant
for such short molecules. In this geometry, the effective persistence length of the shortest molecules decreases by a factor
of two compared to the established value for long molecules, and excluded-volume forces extend the molecules to about
one third of their nominal contour lengths in the absence of any external forces. We interpret these results in the
framework of a modified wormlike chain model.
Optical tweezers have become an important tool for the manipulation of single biomolecules. However, their application
to stretching biopolymers is usually limited to molecules that are several microns in length because conventional optical
tweezers manipulate molecules laterally in the focal plane of the microscope objective, a mode in which steric
hindrances from the attached microsphere and the surface are substantial. In order to study the properties of short DNA
fragments that are typically 1000 bp long, we used optical tweezers in the axial direction to pull microsphere away from
the cover glass surface. The microsphere was held in the linear region of the optical potential where the optical force is
least sensitive to the bead position. By varying the laser intensity, different stretching forces were applied to the DNA
molecule, and the axial position of the tethered microsphere was obtained from its diffraction pattern. The results
indicate that the wormlike chain model is still valid for such short DNA fragments.
Most wireless sensor networks base their design on an ad hoc (multi-hop) network technology that focus on organizing and maintaining a network formed by a group of moving objects with a communication device in an area with no fixed base stations or access points. Although ad hoc network technologies are capable of constructing a sensor network, the design and implementation of sensor networks for monitoring stationary nodes such as construction sites and nature-disaster-prone areas can be furthered simplified to reduce power consumption and overhead. Based on the nature of immobile nodes, a hierarchical sensor network architecture and its associated communication protocols are proposed in this paper. In this proposed architecture, most elements in the sensor network are designed to be equipped with no functions for message forwarding or channel scheduling. The local control center uses a centralized communication protocol to communicate with each sensor node. The local control center can also use ad hoc network technology to relay the data between each of the sensors. This approach not only minimizes the complexity of the sensor nodes implemented but also significantly reduces the cost, size and power consumption of each sensor node. In addition, the benefit of using ad-hoc network technology is that the local controller retains its routing capabilities. Therefore, power efficiency and communication reliability can be both achieved and maximized by this type of hierarchical sensor network.
A newly developed smart sensor node that can monitor the safety of temporary structures such as scaffolds at construction sites is detailed in this paper. The design methodology and its trade-offs, as well as its influence on the optimization of sensor networks, is examined. The potential impact on civil engineering construction sites, environmental and natural disaster pre-warning issues, etc., all of which are foundations of smart sensor nodes and corresponding smart sensor networks, is also presented. To minimize the power requirements in order to achieve a true wireless system both in terms of signal and power, a sensor node was designed by adopting an 8051-based micro-controller, an ISM band RF transceiver, and an auto-balanced strain gage signal conditioner. With the built-in RF transceiver, all measurement data can be transmitted to a local control center for data integrity, security, central monitoring, and full-scale analysis. As a battery is the only well-established power source and there is a strong desire to eliminate the need to install bulky power lines, this system designed includes a battery-powered core with optimal power efficiency. To further extend the service life of the built-in power source, a power control algorithm has been embedded in the microcontroller of each sensor node. The entire system has been verified by experimental tests on full-scale scaffold monitoring. The results show that this system provides a practical method to monitor the structure safety in real time and possesses the potential of reducing maintenance costs significantly. The design of the sensor node, central control station, and the integration of several kinds of wireless communication protocol, all of which are successfully integrated to demonstrate the capabilities of this newly developed system, are detailed. Potential impact to the network topology is briefly examined as well.
KEYWORDS: Sensors, Amplifiers, Signal detection, Signal processing, Telecommunications, Information technology, Self-assembled monolayers, Receivers, Nanotechnology, Interfaces
Attempts to develop a Wireless Health Advanced Mobile Bio-diagnostic System (abbreviated as WHAM-BioS) have arisen from the need to monitor the health status of patients under long-term care programs. The proposed WHAM-BioS as presented here was developed by integrating various technologies: nano/MEMS technology, biotechnology, network/communication technology, and information technology. The biochips proposed not only detect certain diseases but will also report any abnormal status readings on the patient to the medical personnel immediately through the network system. Since long-term home care is typically involved, the parameters monitored must be analyzed and traced continuously over a long period of time. To minimize the intrusion to the patients, a wireless sensor embedded within a wireless network is highly recommended. To facilitate the widest possible use of various biochips, a smart sensor node concept was implemented. More specifically, various technologies and components such as built-in micro power generators, energy storage devices, initialization processes, no-waste bio-detection methodologies, embedded controllers, wireless warning signal transmissions, and power/data management were merged and integrated to create this novel technology. The design methodologies and the implementation schemes are detailed. Potential expansions of this newly developed technology to other applications regimes will be presented as well.
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