New insights for using self-assembly materials to improve the detection stability in label-free DNA-chip and immuno-sensors

Abstract

a b s t r a c tThis 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.

Memristive-biosensors: A new detection method by using nanofabricated memristors

“…The current properties of dried organic samples are affected by humidity [32], too. Water molecules adsorbed from humid environment into thin organic films have been measured with both hydrophilic [34] and hydrophobic [33] molecules. Therefore, all the data we reported in Sections 3.2 and 3.3 were acquired in highly controlled conditions dealing with temperature and humidity.…”

A new ethylene glycol-silane monolayer for highly-specific DNA detection on Silicon Chips

“…The strong role played by the new proposed precursor films in highlyspecific DNA detection relies in two molecular features: the methoxyl groups and the ethylene-glycol chains. The ethylene-glycol chains coordinate water molecules, as envisaged by ab initio calculations [14] and confirmed by both infrared spectroscopy [15] and QCM [6]. Furthermore, non-specific adsorption of DNA onto the ethylene-glycol was only obtained when the SAM was formed using only the anchoring silanes, without mixing with the repelling ones.…”

“…These conductive pathways affect the capacitance detection and cause time instabilities and large detection errors. Capacitance DNA detection onto gold has been highly-improved by using ethylene-glycol thiol monolayers as precursors for probe anchoring [6]. These films do not show deep grooves crossing the film in the structure at the nano-scale [7].…”

An Outlook on Design Technologies for Future Integrated Systems

“…These techniques are bulky and hard to integrate in a monolithic chip. For this reason, nonlabeled sensing techniques have been proposed, where the matching of a sample to a probe creates a reaction (e.g., redox) yielding a variation of an electrical quantity (e.g., impedance, capacitance, current) that then can be measured by placing the sensor under the probe itself [13], [19], [85]. With this technology, it is possible to integrate sensing with readout electronics and signal processing on the same substrate [55], [117], [122].…”