Cagri A. Savran

Laser-treated hydrophobic paper: an inexpensive microfluidic platform

We report a method for fabricating inexpensive microfluidic platforms on paper using laser treatment. Any paper with a hydrophobic surface coating (e.g., parchment paper, wax paper, palette paper) can be used for this purpose. We were able to selectively modify the surface structure and property (hydrophobic to hydrophilic) of several such papers using a CO(2) laser. We created patterns down to a minimum feature size of 62±1 µm. The modified surface exhibited a highly porous structure which helped to trap/localize chemical and biological aqueous reagents for analysis. The treated surfaces were stable over time and were used to self-assemble arrays of aqueous droplets. Furthermore, we selectively deposited silica microparticles on patterned areas to allow lateral diffusion from one end of a channel to the other. Finally, we demonstrated the applicability of this platform to perform chemical reactions using luminol-based hemoglobin detection.

Diffractometric detection of proteins using microbead-based rolling circle amplification

We present a robust, sensitive, fluorescent- or radiolabel-free self-assembled optical diffraction biosensor that utilizes rolling circle amplification (RCA) and magnetic microbeads as a signal enhancement method. An aptamer-based sandwich assay was performed on microcontact-printed streptavidin arranged in 15 microm wide alternating lines and could specifically capture and detect platelet-derived growth factor B-chain (PDGF-BB). An aptamer served as a template for the ligation of a padlock probe, and the circularized probe could in turn be used as a template for RCA. The concatameric RCA product hybridized to biotinylated oligonuclotides which then captured streptavidin-labeled magnetic beads. In consequence, the signal from the captured PDGF-BB was amplified via the concatameric RCA product, and the diffraction gratings on the printed areas produced varying intensities of diffraction modes. The detected diffraction intensity and the density of the microbeads on the surface varied as a function of PDGF-BB concentration. Our results demonstrate a robust biosensing platform that is easy to construct and use and devoid of fluorescence microscopy. The self-assembled bead patterns allow both a visual analysis of the molecular binding events under an ordinary bright-field microscope and serve as a diffraction grating biosensor.

Real-time detection of airborne viruses on a mass-sensitive device

We present real-time detection of airborne Vaccinia viruses using quartz crystal microbalance (QCM) in an integrated manner. Vaccinia viruses were aerosolized and neutralized using an electrospray aerosol generator, transported into the QCM chamber, and captured by a QCM crystal. The capture of the viruses on the QCM crystal resulted in frequency shifts proportional to the number of viruses. The capture rate varied linearly with the concentration of initial virus suspensions (8.5x10(8)-8.5x10(10) particlesml) at flow rates of 2.0 and 1.1 lmin. This work demonstrates the general potential of mass sensitive detection of nanoscale biological entities in air.

In situ assembled diffraction grating for biomolecular detection

The authors report experiments with a diffraction-based biosensor based on self-assembly of target-containing nanobeads that form optical diffraction gratings. They demonstrate that the diffraction signal is a function of the bead size, and that noise is minimized by normalizing the intensities of the diffraction modes. They characterize the dependence of the diffraction signal on equivalent bead size and demonstrate the potential of the scheme in detecting biologically significant molecules.

Circulating tumor cell detection using a parallel flow micro-aperture chip system

We report on-chip isolation and detection of circulating tumor cells (CTCs) from blood samples using a system that integrates a microchip with immunomagnetics, high-throughput fluidics and size-based filtration. CTCs in a sample are targeted via their surface antigens using magnetic beads functionalized with antibodies. The mixture is then run through a fluidic chamber that contains a micro-fabricated chip with arrays of 8 μm diameter apertures. The fluid runs parallel to the microchip while a magnetic field is generated underneath to draw the beads and cells bound to them toward the chip surface for detection of CTCs that are larger than the apertures and clear out free beads and other smaller particles bound to them. The parallel flow configuration allows high volumetric flow rates, which reduces nonspecific binding to the chip surface and enables multiple circulations of the sample fluid through the system in a short period of time. In this study we first present models of the magnetic and fluidic forces in the system using a finite element method. We then verify the simulation results experimentally to determine an optimal flow rate. Next, we characterize the system by detecting cancer cell lines spiked into healthy human blood and show that on average 89% of the spiked MCF-7 breast cancer cells were detected. We finally demonstrate detection of CTCs in 49 out of 50 blood samples obtained from non-small cell lung cancer (NSCLC) patients and pancreatic cancer (PANC) patients. The number of CTCs detected ranges from 2 to 122 per 8 mL s of blood. We also demonstrate a statistically significant difference between the CTC counts of NSCLC patients who have received therapy and those who have not.

Rapid Detection of S‐Adenosyl Homocysteine Using Self‐Assembled Optical Diffraction Gratings

Quantitative characterization of biomolecules is critical for molecular diagnostics and drug development. Several assays based on spectrophotometry, fluorometry, chemiluminescence, and electrochemical immunoassays have been reported for biomolecular detection. These methods are often slow owing to multiple sample pretreatment steps that increase analysis time and cost. Immunoassays that combine high sensitivity with fast, robust, and inexpensive methods for biomolecular detection are of growing importance. Herein the development of a self-assembled optical diffraction biosensor is described which is devoid of microfabrication or enzymatic amplification for the rapid detection of S-adenosyl homocysteine (SAH), a potential diagnostic marker for cardiovascular disease, with a sensitivity limit of 24.5 pgmL . SAH is a low-molecular-mass analyte (384 Da) consisting of the nucleoside adenine joined to the amino acid homocysteine (Hcy) by a 5’ thioether linkage. Our method relies on a sandwich-binding approach, wherein SAH is bound by an antibody through the Hcy moiety while an adenine-specific RNA aptamer binds to the adenine moiety (Figure 1). We designed a strategy using antibody-coupled (Ab) beads to capture SAH from solution in addition to aptamerfunctionalized micropatterns specific for adenine which are stamped on a gold-coated glass slide (gold chip). Based on these specific interactions, SAH bound to the Ab beads produces a self-assembled optical diffraction grating upon exposure to the aptamer-functionalized micropatterns (Figure 2). The high-affinity adenosine-specific aptamer containing the 39-mer sequence CGG AUG AGA CGC UUG GCG UGU GCU GUG GAG AGU CAU CCG was chosen

Bright-field analysis of phi29 DNA packaging motor using a magnetomechanical system

We report a simple and robust magnetomechanical system for direct visual observation of the DNA packaging behavior of the bacteriophage phi29 in real time. The system comprises a micron-sized magnetic bead attached to the free end of the viral DNA, a magnet and a bright-field microscope. We show that the phi29 DNA packaging activity can be observed and dynamically analyzed at the single molecular level in bright field with a relatively simple system. With this system we also visually demonstrate the phi29 motor transporting a cargo 10 000 times the viral size.

Nanomechanical biosensing with immunomagnetic separation

We report a biosensing method that combines immunomagnetic separation and nanomechanical detection. In this method, same magnetic beads that are used to “fish” biomolecules from complex mixtures enable deflection of a cantilever structure upon excitation by an oscillating magnetic field. Biotin-coated magnetic beads were used to capture and separate streptavidin from serum. Streptavidin loaded magnetic beads were exposed to a differential cantilever system whose sensing arm was functionalized with biotin. The magnetic force applied on the streptavidin-beads resulted in differential cantilever deflections that could be detected down to 0.26 Arms in air.

A Compact Manually Actuated Micromanipulator

This letter reports a compact, versatile, and user-friendly micromanipulator that uses an elastically deformable silicon microtweezer to grab microentities, and a micrometer head for rotational manual actuation. The micro-/macroconnection is achieved via a graphite interface that results in a compact and portable design and placement on most translation stages. The system which can operate in both air and liquid, and transport objects between the two media, has a wide range of applications. We demonstrate but a few of them, including in situ construction of microstructures in 3-D, isolation and placement of individual microparticles on designated spots on sensors, on-demand microcontact printing of microparticles, and manipulation of live stem cell spheres.

Reflective Diffraction Gratings From Hydrogels as Biochemical Sensors

We report reflective diffraction gratings made from smart hydrogels for ultrasensitive biochemical detection. As an example for a stimuli-responsive hydrogel, we chose a pH-sensitive hydrogel to construct diffraction gratings that swell/shrink reversibly due to changes in pH. Interferometric analysis of the grating enabled detection of the hydrogels motions with nanoscale precision and resulted in a resolution of 6 × 10-4 pH units. The developed system is remarkably simple both to fabricate and operate, and yet extremely sensitive. Moreover, the concept of the reflective hydrogel grating is generic and can be applied detection of a wide range of other stimuli.