Lukas Brandhoff

An Infrared Absorbance Sensor for the Detection of Melanoma in Skin Biopsies

An infrared (IR) absorbance sensor has been designed, realized and tested with the aim of detecting malignant melanomas in human skin biopsies. The sensor has been designed to obtain fast measurements (80 s) of a biopsy using a small light spot (0.5 mm in diameter, typically five to 10 times smaller than the biopsy size) to investigate different biopsy areas. The sensor has been equipped with a monochromator to record the whole IR spectrum in the 3330–3570 nm wavelength range (where methylene and methyl stretching vibrations occur) for a qualitative spectral investigation. From the collected spectra, the CH2 stretch ratio values (ratio of the absorption intensities of the symmetric to asymmetric CH2 stretching peaks) are determined and studied as a cancer indicator. Melanoma areas exhibit different spectral shapes and significantly higher CH2 stretch ratios when compared to healthy skin. The results of the infrared investigation are compared with standard histology. This study shows that the IR sensor is a promising supportive tool to improve the diagnosis of melanoma during histopathological analysis, decreasing the risk of misdiagnosis.

A multi-purpose ultrasonic streaming mixer for integrated magnetic bead ELISAs

We present an ultrasonic streaming mixer for disposable and on-chip magnetic bead ELISAs. The ultrasonic transducer is placed at system-level to keep cost per chip as low as possible, and is coupled to the chip by means of a solid ultrasonic horn. The system provides mixing of liquids, as well as dispersion of the superparamagnetic beads in the ELISA. Additionally it can be used clean the chamber surface from nonspecifically bound proteins during the washing steps in the ELISA protocol. Using our system the time for the ELISA protocol has been greatly reduced down to 30 min.

Removal of nonspecific bindings in on-chip ELISAs with low power ultrasound

We present a novel method for removing nonspecifically bound proteins for on-chip ELISAs (Enzyme-Linked-Immuno-Sorbent-Assays) by integrated ultrasonic washing of the reaction chamber. Low power ultrasound is concentrated into the reaction chamber with an ultrasonic horn contained in the base of the measurement system. Application of ultrasonication during the last washing step of the ELISA protocol removes adsorbed proteins from the wall while not affecting specifically bound analytes. This method reduces the cost of the disposable assay-chips, while delivering comparable results with standard blocking methods.

Creation of hydrophilic microfluidic devices for biomedical application through stereolithography

We present a method to graft a layer of poly-ethylene-glycol (PEG) to the surface of stereo-lithography fabricated or 3D-printed microfluidic devices rendering it hydrophilic and repellent to the adhesion of proteins. The PEG forms a rigid bond with the surface that is more stable than many coatings or surface treatments. This makes stereolithography much more attractive as a prototyping platform for microfluidics. The method has been proven with two different resins by different manufacturers, showing the universality of said treatment.

A biopsymeter to support the diagnostic procedure of skin samples

We present an infrared biopsymeter to assist pathologists in the diagnosis of melanoma presence in skin biopsies. The designed and realized system combines the features of visual inspection and physical sensing to reduce false positives and false negatives occurring during standard histopathological analyses. The biopsymeter determines the CH2-stretch ratio by infrared absorbance measurements of skin biopsies. Investigations conducted with the biopsymeter shows that malignant melanomas and melanoma metastases have higher CH2-stretch ratio values compared to healthy skin tissues.

Running Droplet Optical Multiplexer

Abstract We present an optofluidic device for switching light from multiple inputs to one common output. The device uses a microfluidic channel filled with high index of refraction oil as a waveguide, and moves low refractive index interruptions in the form of aqueous droplets through the channel. Whenever a droplet passes one of the optical inputs, this specific input is switched through to the output. This produces a running switching of one output following the other creating a 8x1 multiplexer.

Optofluidic out-of-plane interferometer

We present a Rayleigh interferometer with a novel optofluidic retarder, using precisely controlled and mixed fluids that vary the optical path length in one arm. The retarder is built as a PDMS device, including on chip mixing of the retardation liquid. The out-of-plane geometry facilitates the inclusion in generic optical systems, and presents a major advantage over traditional in-plane optofluidics. To our knowledge this is the first device using out-of-plane optofluidics to manipulate light for interferometry applications.