V. Tsouti

Liquid phase direct laser printing of polymers for chemical sensing applications

This letter demonstrates the direct laser printing of polymers on capacitive micromechanical arrays for the realization of a chemical sensor. Each sensor of a single chip array is composed of a thin Si membrane covered by a chemically sensitive polymer layer by means of a direct laser printing technique. We present the high spatial resolution deposition of three different sensitive polymer materials by the liquid phase laser induced forward transfer process. We also show that the optimum sensitivity of the sensors can be achieved by varying the percentage of the coverage of the sensors’ membranes with the polymer.

Capacitive microsystems for biological sensing

The growing interest in personalized medicine leads to the need for fast, cheap and portable devices that reveal the genetic profile easily and accurately. To this direction, several ideas to avoid the classical methods of diagnosis and treatment through miniaturized and label-free systems have emerged. Capacitive biosensors address these requirements and thus have the perspective to be used in advanced diagnostic devices that promise early detection of potential fatal conditions. The operation principles, as well as the design and fabrication of several capacitive microsystems for the detection of biomolecular interactions are presented in this review. These systems are micro-membranes based on surface stress changes, interdigitated micro-electrodes and electrode-solution interfaces. Their applications extend to DNA hybridization, protein-ligand binding, antigen-antibody binding, etc. Finally, the limitations and prospects of capacitive microsystems in biological applications are discussed.

Detection of DNA mutations using a capacitive micro-membrane array

The detection of DNA hybridization using capacitive readout and a biosensor array of ultrathin Si membranes is presented. The biosensor exploits the ability of the ultrathin membranes to deflect upon surface stress variations caused by biological interactions. Probe DNA molecules are immobilized on the membrane surface and the surface stress variations during hybridization with their complementary strands force the membrane to deflect and effectively change the capacitance between the flexible membrane and the fixed substrate. The sensor array comprises 256 such sensing sites thus allowing the concurrent sensing of multiple DNA mutations. The biosensor and its performance for the detection of complementary DNA strands are demonstrated using beta-thalassemia oligonucleotides. The experimental results show that the presented sensors are able to detect DNA hybridization and to discriminate single nucleotide mismatches.

Integrated biochip for PCR-based DNA amplification and detection on capacitive biosensors

Responding to an increasing demand for LoC devices to perform bioanalytical protocols for disease diagnostics, the development of an integrated LoC device consisting of a μPCR module integrated with resistive microheaters and a biosensor array for disease diagnostics is presented. The LoC is built on a Printed Circuit Board (PCB) platform, implementing both the amplification of DNA samples and DNA detection/identification on-chip. The resistive microheaters for PCR and the wirings for the sensor read-out are fabricated by means of standard PCB technology. The microfluidic network is continuous-flow, designed to perform 30 PCR cycles with heated zones at constant temperatures, and is built onto the PCB utilizing commercial photopatternable polyimide layers. Following DNA amplification, the product is driven in a chamber where a Si-based biosensor array is placed for DNA detection through hybridization. The sensor array is tested for the detection of mutations of the KRAS gene, responsible for colon cancer.

A capacitive biosensor based on ultrathin Si membranes

A biosensor which takes advantage of surface stress changes during biological interactions and is able to translate them into a capacitive signal is presented. The sensor consists of an ultrathin silicon membrane on which receptor molecules are immobilized. During biomolecular interactions, the surface stress changes and the membrane deflects resulting in a change in device capacitance. The biosensor is part of a 16 times 16 array thus allowing for the making of larger assays with the concurrent sensing of multiple biological targets. First results using the biotin-steptavidin system are presented.

Sensitivity investigations of surface stress capacitive DNA sensor

Investigations of the sensitivity and selectivity of a capacitive type biosensor array, consisting of a total of 256 biosensing elements, in the detection of single oligonucleotide mutations is presented. The biosensor takes advantage of surface stress changes during biological interactions and is able to translate them into a capacitive signal. The array is organized in a 16×16 matrix of distinct biosensing elements thus allowing for the concurrent sensing of multiple biological targets. In this work the sensing elements of the array are spotted with three different oligonucleotides (CD8, CD17 and CD19) and their hybridization is detected using 36nM PCR. Moreover tests with CD19 revealed the ability of the biosensor to detect the hybridization of the oligo with sample concentrations of 36, 18 and 9nM.