Planar Junctionless Field-Effect Transistor for Detecting Biomolecular Interactions.

Label-free field-effect transistor-based immunosensors are promising candidates for proteomics and peptidomics-based diagnostics and therapeutics due to their high multiplexing capability, fast response time, and ability to increase the sensor sensitivity due to the short length of peptides. In this work, planar junctionless field-effect transistor sensors (FETs) were fabricated and characterized for pH sensing. The device with SiO2 gate oxide has shown voltage sensitivity of 41.8 ± 1.4, 39.9 ± 1.4, 39.0 ± 1.1, and 37.6 ± 1.0 mV/pH for constant drain currents of 5, 10, 20, and 50 nA, respectively, with a drain to source voltage of 0.05 V. The drift analysis shows a stability over time of -18 nA/h (pH 7.75), -3.5 nA/h (pH 6.84), -0.5 nA/h (pH 4.91), 0.5 nA/h (pH 3.43), corresponding to a pH drift of -0.45, -0.09, -0.01, and 0.01 per h. Theoretical modeling and simulation resulted in a mean value of the surface states of 3.8 × 1015/cm2 with a standard deviation of 3.6 × 1015/cm2. We have experimentally verified the number of surface sites due to APTES, peptide, and protein immobilization, which is in line with the theoretical calculations for FETs to be used for detecting peptide-protein interactions for future applications.

Towards microfluidic sperm refinement: impedance-based analysis and sorting of sperm cells.

The use of high quality semen for artificial insemination in the livestock industry is essential for successful outcome. Insemination using semen with a high number of sperm cells containing morphological defects has a negative impact on fertilization outcome. Therefore, semen with a high number of these abnormal cells is discarded in order to maintain high fertilization potential, resulting in the loss of a large number of morphologically normal sperm cells (up to 70-80% of original sample). A commonly occurring morphological sperm anomaly is the cytoplasmic droplet on the sperm flagella. Currently, no techniques are available to extract morphologically normal sperm cells from rejected samples. Therefore, we aim to develop a microfluidic setup which is able to detect and sort morphologically normal sperm cells label-free and non-invasively. In a proof-of-concept experiment, differential impedance measurements were used to detect the presence of cytoplasmic droplets on sperm flagella, which was quantified by calculating the area under the curve (AUC) of the corresponding impedance peaks. A receiver operating characteristic curve of this electrical analysis method showed the good predictive power of this analysis method (AUC value of 0.85). Furthermore, we developed a label-free cell sorting system using LabVIEW, which is capable of sorting sperm cells based on impedance. In a proof-of-concept experiment, sperm cells and 3 µm beads were sorted label-free and non-invasively using impedance detection and dielectrophoresis sorting. These experiments present our first attempt to perform sperm refinement using microfluidic technology.

Microfluidic single sperm entrapment and analysis.

Selection of healthy spermatozoa is of crucial importance for the success rates of assisted reproduction technologies (ART) such as in vitro fertilization and intra-cytoplasmic sperm injection. Although sperm selection for ART procedures is predominantly based on sperm motility, successful fertilization is not predicted by good motility alone. For example, sperm characteristics such as the acrosome state and DNA integrity have shown significant impact on ART outcome. Although fertilization can be achieved with a single spermatozoon of high quality, current quality assessments are population-based and do not allow investigation of multiple sperm characteristics on a single spermatozoon simultaneously. In order to study sperm cells on the single cell level, we designed and characterized a PDMS microfluidic platform that allows single sperm entrapment. After spatially confining individual sperm cells within microfluidic cell traps, the cell viability, chromosomal content and acrosome state were studied. This platform is suitable for the analysis of individual sperm cells, which could be exploited for (non-invasive) sperm analysis and selection by impedance or Raman spectroscopy.

Make it spin: individual trapping of sperm for analysis and recovery using micro-contact printing.

In this article, we describe the development of a high throughput platform to spatially manipulate viable sperm for motility measurements and recovery of the best single sperm for fertilization purposes. Micro-contact printing was used to pattern islands of adhesive proteins (fibronectin) separated by sperm repellent species (Pluronic acid F-127) on commercially available polystyrene substrates. Following washing, arrays of viable single sperm were captured onto the islands demonstrating for the first time that sperm can be trapped by micro-contact printing with patterning efficiency of 90% while retaining 100% viability. These were then subjected to motility analysis whilst remaining spatially confined to the islands. Single sperm motility was assessed (n = 37) by software analysis measuring the number of rotations per second (degrees s⁻¹). The assignment of array coordinates allows the more active single sperm to be easily identified and recovered by a simple micromanipulator pipette aspiration step with automated possibility for assisted reproductive technologies or further quality correlation analysis. Taken together, we show for the first time a technique to simultaneously screen thousands of viable single sperm for motility assessment while retaining the ability for single species recovery for enhanced fertilization purposes.

Painful paediatric hip: frog-leg lateral view only!

OBJECTIVE: For hip complaints in the paediatric population, it is common practice to acquire both anteroposterior (AP) and frog-leg lateral (FL) radiographs. This combination of views provides a high diagnostic yield, but also doubles radiation exposure. We investigated the diagnostic accuracy of obtaining a solitary FL view as compared to a combination of the AP and FL view. METHODS: Hip radiographs of 524 children (aged 2-15 years) referred for acute hip pain were retrospectively assessed by two independent radiologists. Cases of trauma, neuromuscular disorders or a history of known hip disease were excluded. Radiologists were blinded to the AP radiograph while assessing the solitary FL radiograph. We used Cohen's kappa test to calculate agreement between the assessment of both views and the solitary FL view. RESULTS: Agreement between the assessment of the solitary FL view and the combination of the AP and FL view was very high with a kappa value of 0.989. CONCLUSION: The diagnostic accuracy of the FL radiograph in cases of hip complaints in children is as high as the current standard employing both AP and FL views. Therefore a solitary FL radiograph appears sufficient. This practice would substantially reduce radiation exposure. KEY POINTS: • Radiation exposure in children should be kept to a minimum. • In paediatric hip radiography a solitary frog-leg lateral view suffices. • This reduces radiation exposure and costs of imaging.

Electronic collimation and radiation protection in paediatric digital radiography: revival of the silver lining.

In digital radiography we are now able to electronically collimate images after acquisition. This may seem convenient in paediatric imaging, but we have to be aware that electronic collimation has two major downsides. Electronic collimation implicates that the original field size should have been smaller and the child has been exposed to unnecessary radiation. Also, by use of electronic collimation, potentially important information may be lost. The "silver lining", denoting the X-ray beam collimation, can serve as a useful radiation protection instrument to check for proper field size and detect unnecessary exposure. Furthermore, the silver lining confirms all exposed anatomy is shown in the final image, and thus may also serve as a quality assurance instrument as the patient has the right to all acquired information. Teaching Points • The ability to electronically collimate an image after acquisition may serve to enhance contrast in the region of interest. • The ability to electronically collimate an image after acquisition carries the risk of overexposure. • The ability to electronically collimate an image after acquisition carries the risk of losing important information. • The silver lining can serve as a quality control instrument for proper collimation. • The patient has the right to all information obtained during an X-ray examination.

Integrated electrochemical sensor array for on-line monitoring of yeast fermentations.

This paper describes the design, modeling, and experimental characterization of an electrochemical sensor array for on-line monitoring of fermentor conditions in both miniaturized cell assays and in industrial scale fermentations. The viable biomass concentration is determined from impedance spectroscopy. As a miniaturized electrode configuration with high cell constant is applied, the spectral conductivity variation is monitored instead of the permittivity variation. The dissolved oxygen concentration is monitored amperometrically using an ultramicroelectrode array, which is shown to have negligible flow dependence. pH is monitored using an ion-sensitive field effect transistor (ISFET), and a platinum thermistor is included for temperature measurements. All sensors were shown to be sufficiently accurate within the range relevant to yeast fermentations. The sensor array is shown to be very stable and durable and withstands steam-sterilization.

Strongly accelerated and humidity-independent drying of nanochannels induced by sharp corners.

Measurements are shown indicating that the drying rate of nanochannels can be enhanced by up to 3 orders of magnitude relative to drying by vapor diffusion, and that the drying rate is independent of the relative humidity of the environment up to a relative humidity of more than 90%. Micromachined Pyrex glass nanochannels of 72 nm height and with sharp corners (corner angles 7 degrees) were used. Available theory shows that the sharp corners function as a low-resistance pathway for liquid water, siphoning (wicking) the water to a location close to the channel exit before it evaporates. The described phenomena are of importance for the understanding of drying processes in industry and agriculture. The introduction of sharp corners or grooves can furthermore be beneficial for the functioning of microheat pipes and capillary-pumped loops.

A miniaturized carbon dioxide gas sensor based on sensing of pH-sensitive hydrogel swelling with a pressure sensor.

A measurement concept has been realized for the detection of carbon dioxide, where the CO(2) induced pressure generation by an enclosed pH-sensitive hydrogel is measured with a micro pressure sensor. The application of the sensor is the quantification of the partial pressure of CO(2) (Pco(2)) in the stomach as diagnosis for gastrointestinal ischemia. The principle is put to the proof by examining the sensor response to changes in Pco(2). Furthermore, the response time, temperature-sensitivity and resolution are determined. The sensor responds well to changes in Pco(2) with a maximum pressure generation of 0.29 x 10(5) Pa at 20 kPa CO(2). The 90% response time varies between 1.5 and 4.5 minutes at 37( composite function)C. The sensor shows a linear temperature-sensitivity which can easily be compensated for, and enables detection of Pco(2) changes as small as 0.5 kPa CO(2).