title: New insights for using self-assembly materials to improve the detection stability in label-free DNA-chip and immuno-sensors.
abstract: This paper examines reliable advancements in low-cost DNA- and immuno-chips. Capacitance detection was successfully chosen to develop label-free bio-chips. Probe immobilization was rigorously investigated in order to obtain reliable capacitance measurements. Protein probes immobilized by using usual alkanethiols or thiolated ssDNA probes directly immobilized on gold do not allow sufficient stable capacitance measurements. New alkanethiols improved with ethylene-glycol function are shown in this paper to be more suitable materials for capacitive bio-chip development. Atomic Force Microscopy, Quartz Crystal Microbalance, and Capacitance Measurements were used to demonstrate that ethylene-glycol alkanethiols allow high time stability, smaller errors in detection, and improved ideal behaviour of the sensing surfaces. Measured capacitance is in the range of 8-11 nF/mm(2) for antibody layers and close to 6 nF/mm(2) for DNA probes. It is in the range of 10-12 nF/mm(2) and of 4-6 nF/mm(2) for antigen and DNA detection, respectively. The percentage error in detection is highly improved and it is in the range of 11-37% and of 0,23-0,82% for antigen and DNA, respectively. The reproducibility is also improved and it is close to 0,44% for single spot measurements on ethylene-glycol alkanethiols. A molecular theory attributing these improvements to water molecules strongly coordinated by ethylene-glycol functional groups and to solution ions not entering into probe films is finally proposed.
authors.affiliation: Biochemistry Department G.Moruzzi, University of Bologna, Bologna, Italy. sandro.carrara@epfl.ch
authors.forename: Sandro
authors.initials: S
authors.lastname: Carrara
authors.forename: Luca
authors.initials: L
authors.lastname: Benini
authors.forename: Vijayender
authors.initials: V
authors.lastname: Bhalla
authors.forename: Claudio
authors.initials: C
authors.lastname: Stagni
authors.forename: Anna
authors.initials: A
authors.lastname: Ferretti
authors.forename: Andrea
authors.initials: A
authors.lastname: Cavallini
authors.forename: Bruno
authors.initials: B
authors.lastname: Riccò
authors.forename: Bruno
authors.initials: B
authors.lastname: Samorì
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D015374:Biosensing Techniques / Q000295:instrumentation*; D025802:Electric Capacitance; D004563:Electrochemistry / Q000295:instrumentation*; D007118:Immunoassay / Q000295:instrumentation*; D020411:Oligonucleotide Array Sequence Analysis / Q000295:instrumentation*; D012680:Sensitivity and Specificity; D013194:Staining and Labeling
chemical_list: D001672:Biocompatible Materials