Utilizing photothermally induced oscillation damping parameters for the determination of bacterial load suspended in microfluidic resonators

Microchannel resonators containing a miniaturized volume of a solution can have various applications in different fields. In this study, a microchannel cantilever was loaded with a solution containing a very small number of Pseudomonas fluorescens bacteria suspended in M9 growth medium. The liquid-filled microchannel cantilever was irradiated with a 532-nm laser. The shift in the frequency of the cantilever due to varying bacterial loads is less reliable; therefore, it could not be used for monitoring the bacterial concentration. The energy loss of the cantilever extracted from the quality factor exhibited reliable results and a very strong correlation with the bacterial concentration. The results showed a linear relation between the damping factor of the cantilever and the bacterial concentration. Accordingly, these findings were expected because the bacteria inside the solution can be considered as particles acting against the cantilever motion due to the solution’s viscosity. Thus, more bacteria caused more damping, in agreement with the experimental observations. A semiquantitative experiment was conducted with a heat source (i.e., laser beam) that focused at the cantilever tip to demonstrate the redistribution of the bacterial load within the solution due to the thermal gradient

Cantilever systems for the next generation of biomechanical sensors

Ieder interactief systeem gebruikt apparaten om informatie over de omgeving te verkrijgen. Ook de mens gebruikt apparaten om zijn omgeving te onderzoeken; tast- en gehoor-apparatuur voor mechanische impulsen, zicht- voor elektromagnetische en smaak- en reuk- voor chemische eigenschappen. Het gaat om thermometers, microfoons, ccd camera’s, enzovoort: allemaal sensoren die onze waarnemingsmogelijkheden vergroten, prestaties verbeteren en soms zelfs de mens vervangen in autonome systemen. In de laatste decennia is door de opkomst van nano- en biotechnologie de ontwikkeling van chemische sensoren, in het bijzonder biosensoren, in een stroomversnelling geraakt. Biosensoren worden gekenmerkt door de aanwezigheid van een biologische component (bv. een antilichaam, enzym of DNA molecuul) die een interactie aangaat met het te detecteren chemische element. Deze interactie wordt omgezet in een macroscopisch signaal welke vervolgens kan worden uitgelezen door een mens of machine. In ons dagelijks leven zijn biosensoren al terug te vinden in de vorm van zwangerschapstesten en glucosemeters, maar ook in minder opvallende toepassingen zoals voedsel- en waterveiligheid. Er zijn echter nog vele gebieden, in het bijzonder in de geneeskunde, waarin biosensoren een belangrijke rol kunnen spelen. In geval van ziekte (eenvoudige griep of allergie tot levensbedreigende kanker) produceert ons lichaam biologische markers, eiwitten, die inzicht kunnen geven in wat er zich in ons lichaam afspeelt. Daardoor kan er een betere inschatting worden gemaakt van de prognose en kan de therapie mogelijk specifiek op de patiënt worden afgestemd. Helaas is vaak niet bekend welke markers een rol spelen, en als dit wel bekend is, is de detectie veelal zeer kostbaar of zelfs niet mogelijk. In my thesis work I investigated alternative geometries of nanomechanical oscillators to be employed as biomolecular sensors. Simple mechanical oscillators, such as cantilevers and double clamped beams have been deeply investigated in the last decade and single molecule sensitivity was demonstrated. However, beside few marginal exceptions, the proof of principle demonstrations did not yet evolve into commercial devices. Alternative geometries can, in principle, improve the simple micromechanical systems studied so far, with more complex transfer functions suitable to operate also in demanding environments. The thesis work was divided in two major sections. In the first section twin cantilevers are discussed. Couples of cantilevers facing each other and separated by a nanometer gap may change their resonance response when one or more molecules are absorbed in the gap. Two different geometries have been fabricated and tested. One, with identical cantilevers, takes advantage of the shift in resonance frequency occurring upon molecular detection; the second with asymmetrical cantilevers, uses the shortest one to actuate the motion of the longer one through a molecular link. In the second part the structure of the twin cantilevers is the starting point for creating a spatially confined chemical reaction in the gap between two cantilevers facing each other. This original process is extremely precise and represents an important milestone towards the future realization of complex micro- and nanomechanical systems for biomolecular detection.

Coherent optical transduction of suspended microcapillary resonators for multi-parameter sensing applications

Characterization of micro and nanoparticle mass has become increasingly relevant in a wide range of fields, from materials science to drug development. The real-time analysis of complex mixtures in liquids demands very high mass sensitivity and high throughput. One of the most promising approaches for real-time measurements in liquid, with an excellent mass sensitivity, is the use of suspended microchannel resonators, where a carrier liquid containing the analytes flows through a nanomechanical resonator while tracking its resonance frequency shift. To this end, an extremely sensitive mechanical displacement technique is necessary. Here, we have developed an optomechanical transduction technique to enhance the mechanical displacement sensitivity of optically transparent hollow nanomechanical resonators. The capillaries have been fabricated by using a thermal stretching technique, which allows to accurately control the final dimensions of the device. We have experimentally demonstrated the light coupling into the fused silica capillary walls and how the evanescent light coming out from the silica interferes with the surrounding electromagnetic field distribution, a standing wave sustained by the incident laser and the reflected power from the substrate, modulating the reflectivity. The enhancement of the displacement sensitivity due to this interferometric modulation (two orders of magnitude better than compared with previous accomplishments) has been theoretically predicted and experimentally demonstrated

Microfluidic Tools for Advanced Biomolecular Characterisation

Proteins – the key building blocks of life – are responsible for the majority of the processes behind biological function. To understand what role proteins play in health and disease, how they operate and interact, it is vital to have tools for biomolecular detection, quantification and fundamental physicochemical characterisation. In this thesis, I have focused on the development of new microfluidic approaches enabling quantitative analysis of biomolecules. First, I describe a microfluidic spray device, developed for a controlled deposition of analyte on surfaces. Due to the small micron-scale droplet size, the evaporation happens in a few milliseconds, thus, leaving only the solvent-free solutes. This method has been vital for depositing biomolecules on a scanning-probe microscopy-imaging substrate, enabling quantitative measurements of heterogeneous protein mixtures. Afterwards, I present the spray combination with gravimetric sensors, such as micro-cantilevers, for a label-free protein detection. I show that this technique can be used for a protein-solution concentration measurement in a quantitative manner. Currently, one of the main issues of diagnostic platforms is the analysis of heterogeneous mixtures. A number of protein-separation techniques have been developed; however, most of the characterisation requires an offline analysis which can introduce artefacts and reequilibration. In the second part of this dissertation, I bridge the gap between liquid chromatography, microfluidic characterisation and mechanical-sensor detection. Specifically, I demonstrate the serial combination between liquid chromatography and analyte deposition by a microfluidic spray nozzle. By depositing analytes onto a quartz-crystal microbalance, I perform a specific label-free analysis of protein mixtures. Furthermore, I present a fluidic interface, facilitating a combination of separation at fast liquid flow with microfluidic size and electrophoretic-mobility measurements. This method allows for a simultaneous measurement of molecule size and charge and acts as an additional chromatographic detector. I demonstrate that this method works for both label-free and labelled biomolecule characterisation and suggests ways to perform scalable mass-spectrometry analysis on a chip

Nanomotion Detection-Based Rapid Antibiotic Susceptibility Testing

Rapid antibiotic susceptibility testing (AST) could play a major role in fighting multidrug-resistant bacteria. Recently, it was discovered that all living organisms oscillate in the range of nanometers and that these oscillations, referred to as nanomotion, stop as soon the organism dies. This finding led to the development of rapid AST techniques based on the monitoring of these oscillations upon exposure to antibiotics. In this review, we explain the working principle of this novel technique, compare the method with current ASTs, explore its application and give some advice about its implementation. As an illustrative example, we present the application of the technique to the slowly growing and pathogenic Bordetella pertussis bacteria.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Measuring interactions in fluids with small-cantilever AFM

This thesis describes the design and realization of a small-cantilever AFM, and the application of this instrument to the measurement of hydrophobic forces between nanoscopic surfaces.LEI Universiteit LeidenStichting FOM, Nanoned, NWO, Tips4CellsLIO

Magnetoresistive and Thermoresistive Scanning Probe Microscopy with Applications in Micro- and Nanotechnology

This work presents approaches to extend limits of scanning probe microscopy techniques towards more versatile instruments using integrated sensor concepts. For structural surface analysis, magnetoresistive sensing is introduced and thermoresistive sensing is applied to study nanoscale phonon transport in chain-like molecules. Investigating with these techniques the properties of shape memory polymers, a fabrication method to design application-inspired micro- and nanostructures is introduced