Carl Frederik Werner

Use of Information Visualization Methods Eliminating Cross Talk in Multiple Sensing Units Investigated for a Light-Addressable Potentiometric Sensor

The integration of nanostructured films containing biomolecules and silicon-based technologies is a promising direction for reaching miniaturized biosensors that exhibit high sensitivity and selectivity. A challenge, however, is to avoid cross talk among sensing units in an array with multiple sensors located on a small area. In this letter, we describe an array of 16 sensing units of a light-addressable potentiometric sensor (LAPS), which was made with layer-by-layer (LbL) films of a poly(amidomine) dendrimer (PAMAM) and single-walled carbon nanotubes (SWNTs), coated with a layer of the enzyme penicillinase. A visual inspection of the data from constant-current measurements with liquid samples containing distinct concentrations of penicillin, glucose, or a buffer indicated a possible cross talk between units that contained penicillinase and those that did not. With the use of multidimensional data projection techniques, normally employed in information visualization methods, we managed to distinguish the results from the modified LAPS, even in cases where the units were adjacent to each other. Furthermore, the plots generated with the interactive document map (IDMAP) projection technique enabled the distinction of the different concentrations of penicillin, from 5 mmol L(-1) down to 0.5 mmol L(-1). Data visualization also confirmed the enhanced performance of the sensing units containing carbon nanotubes, consistent with the analysis of results for LAPS sensors. The use of visual analytics, as with projection methods, may be essential to handle a large amount of data generated in multiple sensor arrays to achieve high performance in miniaturized systems.

Light-Addressable Potentiometric Sensors for Quantitative Spatial Imaging of Chemical Species

A light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor, in which a measurement site on the sensing surface is defined by illumination. This light addressability can be applied to visualize the spatial distribution of pH or the concentration of a specific chemical species, with potential applications in the fields of chemistry, materials science, biology, and medicine. In this review, the features of this chemical imaging sensor technology are compared with those of other technologies. Instrumentation, principles of operation, and various measurement modes of chemical imaging sensor systems are described. The review discusses and summarizes state-of-the-art technologies, especially with regard to the spatial resolution and measurement speed; for example, a high spatial resolution in a submicron range and a readout speed in the range of several tens of thousands of pixels per second have been achieved with the LAPS. The possibility of combining this technology with microfluidic devices and other potential future developments are discussed.

(Bio-)chemical Sensing and Imaging by LAPS and SPIM

The light-addressable potentiometric sensor (LAPS) and scanning photo-induced impedance microscopy (SPIM) are two closely related methods to visualise the distributions of chemical species and impedance, respectively, at the interface between the sensing surface and the sample solution. They both have the same field-effect structure based on a semiconductor, which allows spatially resolved and label-free measurement of chemical species and impedance in the form of a photocurrent signal generated by a scanning light beam. In this article, the principles and various operation modes of LAPS and SPIM, functionalisation of the sensing surface for measuring various species, LAPS-based chemical imaging and high-resolution sensors based on silicon-on-sapphire substrates are described and discussed, focusing on their technical details and prospective applications.

Light-Addressable Potentiometric Sensors for (Bio-)chemical Sensing and Imaging

Abstract A light-addressable potentiometric sensor (LAPS) is a chemical sensor based on the field effect in semiconductor. The width of the space-charge layer at the insulator–semiconductor interface responds to the interfacial potential on the sensing surface, which is a function of the analyte concentration. The variation of the capacitance of the space-charge layer is read out in the form of a photocurrent induced by a light probe. This light-addressability allows spatially resolved measurements of the analyte concentration. The article summarizes various aspects of the LAPS, such as the measurement setup, principle of operation, visualization of analyte concentration, as well as visualization of impedance in the scanning photoinduced impedance microscopy (SPIM) mode, spatial and temporal resolutions, functionalization of the sensing surface, and applications.

Restraining the Diffusion of Photocarriers to Improve the Spatial Resolution of the Chemical Imaging Sensor

The chemical imaging sensor is capable of visualizing the ion distribution. The spatial resolution of the chemical image depends on the horizontal diffusion of photocarriers generated by illumination. In this study; a novel optics is designed to realize a hybrid illumination of a ring of constant light and a spot of modulated light. Improved spatial resolution of the order of few tens of microns was successfully demonstrated.

Flexible electrochemical imaging with “zoom-in” functionality by using a new type of light-addressable potentiometric sensor

The light-addressable potentiometric sensor (LAPS) is capable to visualize chemical concentrations above the sensor structure, hence, generating chemical images. To read-out the sensors, a light pointer illuminates the sensor pixel-by-pixel and the resulting photocurrent will be determine. The lateral dimensions of a single pixel and the image resolution can be controlled by shaping the light pointer accordingly. This work demonstrates a flexible method to design on demand light pointers with different shapes and sizes, to carefully balance between measurement time and measurement resolution. This new method can provide large chemical images in a fast manner and provide high resolutions at required locations.