Steven A. Klein

Partition Coefficient Measurements in Picoliter Drops Using a Segmented Flow Microfluidic Device

A microfluidic method to rapidly measure the octanol-water partition coefficient in thousands of individual picoliter drops is described. A T-junction microfluidic chip is used to generate a segmented flow of monodisperse, fluorescein-laden water in octanol carrier fluid. The partitioning of individual drops reaches equilibrium in less than 2 s. Epifluorescence microscopy is used measure the partition coefficient of fluorescein as a function of pH. Results compare well with previous measurements using traditional shake-flask methods. The methods presented here are rapid, provide detailed statistics, and can be run in parallel, enabling the simultaneous partitioning of thousands of compounds for various applications such as drug development, environmental testing, and combinatorial chemistry. Microfluidic partitioning and extraction in picoliter drops may be useful for studying molecules and particles away from their equilibrium state and in cases with limited samples.

Formation of nanopores in suspended lipid bilayers using quantum dots

In this work, nanopores are formed in lipid (DOPC:DOPE) membranes suspended across 150 micron apertures by oligomeric aggregation of 12 nm diameter CdSe quantum dots. The bilayer and quantum dot nanopores are simultaneously characterized by low noise electrical current monitoring and epifluorescence microscopy. Suspended lipid bilayers form high resistance gigaseals (>10 GOhm) that serve as barriers to the migration of charged ions and particles. Oligomeric aggregation of quantum dots is observed on the surface of the suspended lipid bilayer in the presence of charge stabilized quantum dot suspensions, The aggregate forms a nanometer scale pore (~2 nm in diameter) in the bilayer resulting in non-quantal ion current bursts. Migration of net neutral Rhodamine B dye (1.6 nm molecular diameter) across the bilayer is measured only in the presence of the aggregates. Potential applications for the non-lithographic fabrication of bilayer nanopores include biochemical detection, DNA sequencing, or cellular drug delivery.

Improvement in two-frame correlations by confocal microscopy for temporally resolved micro particle imaging velocimetry

An investigation of two-frame micro particle image velocimetry (μPIV) correlations is presented that utilizes a high-speed, spinning disk confocal micro particle image velocimetry (SDμPIV) system. The system uses Nipkow disk confocal epifluorescence microscopy and a high-speed camera to capture unsteady microscale flows using two-frame cross correlations. In μPIV, ensemble averaging is often used to reduce errors due to noise from out-of-focus particles. However, unsteady non-periodic flows require two-frame correlations which can be difficult to achieve with acceptable accuracy using μPIV. The confocal microscope uses pinhole spatial filtering to remove much of the light originating from outside the focal plane, reducing light from out-of-focus particles and improving the accuracy of two-frame cross correlation μPIV. Improvements to two-frame PIV correlations provided by the confocal system are evaluated using the correlation peak signal to noise ratio and universal outlier detection in steady Poiseuille flow as a function of particle volume fraction and focal depth into the channel. We find that the confocal system increases the mean correlation signal to noise ratio for all cases and reduces the fraction of erroneous vectors under conditions where there is a large number of out-of-focus particles. Time-resolved high-speed PIV is demonstrated through the measurement of an example unsteady flow created by an electrokinetic instability.

A scalable process for manufacturing integrated, washable smart garments applied to heart rate monitoring

We present a new method for building wearable electronic and sensor systems in which all components are permanently integrated directly into garments in high volume except for the battery. We discuss the design and construction of the first such fully-integrated sensor system, wearable heart rate monitoring garments (a sports bra, a compression short, and a compression shirt) that are machine washable. We demonstrate that heart rate measurements can be detected by our systems fabric-based electrodes. We also show experimental results from wash testing of the garment. The process described herein can be applied to the construction of computational and sensor systems for healthcare, sports, virtual reality, and first responder and military personnel monitoring, among others.

Contact Pressure and Load Measurement Techniques for Applications in Semiconductor Packaging

Semiconductor packages undergo mechanical loading at various stages of the manufacturing, assembly and test process. Also, during the assembly of the thermal enabling solution in a system environment, mechanical loads are applied to ensure contact of the thermal solution. These loads can be static and/or dynamic in nature, applied over a short or long periods of time. It is important to characterize these applied loads and the resulting contact pressure. However, the measurement of the contact pressure at the interface is complex and requires special techniques without altering the mechanical boundary conditions or the state of stress. In this paper, some of the existing methods used to measure the in-situ load and pressure distribution will be discussed with special attention provided to methods including: pressure-sensitive paper, piezo-resistive based pressure films, and load cells. We will also discuss the applications of these approaches in semiconductor packaging. In the pressure paper technique, a thin film containing microbeads is placed between the interfaces of interest. These microbeads contain colored ink and rupture when a threshold pressure is applied. The intensity and location of the ink provides the magnitude of pressure and its distribution. While these are inexpensive and easy to use, they are single-use and fail to provide real time data. Another method is to use a thin piezo-resistive sensor. While this technique can provide real-time pressure measurements, it is expensive and comes with additional challenges such as hysteresis, aging, and history-dependent response due to the inherent nature of materials used in the sensor. As a result, obtaining accurate and reproducible measurements is quite challenging. In this paper, we describe an experimental method to quantify the challenges and present an approach to mitigate them to achieve highly accurate and repeatable measurements. Lastly, embedded button load cells or dynamic load cells are also used to study mechanical loads a package is experiencing, but they are bulky and hence hard to use especially when space is limited.