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Silicon Nanoribbon FET Sensors: Fabrication, Surface Modification and Microfluidic Integration
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past decade, the field of medical diagnostics has seen an incredible amount of research towards the integration of one-dimensional nanostructures such as carbon nanotubes, metallic and semiconducting nanowires and nanoribbons for a variety of bio-applications. Among the mentioned one-dimensional structures, silicon nanoribbon (SiNR) field-effect transistors (FET) as electro-chemical nanosensors hold particular promise for label-free, real-time and sensitive detection of biomolecules using affinity-based detection. In SiNR FET sensors, electrical transport is primarily along the nanoribbon axis in a thin sheet (< 30 nm) serving as the channel. High sensitivity is achieved because of the large surface-to-volume ratio which allows analytes to bind anywhere along the NR affecting the entire conductivity by their surface charge. Unfortunately, sensitivity without selectivity is still an ongoing issue and this thesis aims at addressing the detection challenges and further proposing effective developments, such as parallel and multiple detection through using individually functionalized SiNRs.We present here a comprehensive study on design, fabrication, operation and device performance parameters for the next generation of SiNR FET sensors towards multiplexed, label-free detection of biomolecules using an on-chip microfluidic layer which is based on a highly cross-linked epoxy. We first study the sensitivity of different NR dimensions followed by analysis of the drift and hysteresis effects. We have also addressed two types of gate oxides (namely SiO2 and Al2O3) which are commonly used in standard CMOS fabrication of ISFETs (Ion sensitive FET). Not only have we studied and compared the hysteresis and response-time effects in the mentioned two types of oxides but we have also suggested a new integrated on-chip reference nanoribbon/microfluidics combination to monitor the long-term drift in the SiNR FET nanosensors. Our results show that compared to Al2O3, silicon-oxide gated SiNR FET sensors show high hysteresis and slow-response which limit their performance only to background electrolytes with low ionic strength. Al2O3 on the other hand proves more promising as the gate-oxide of choice for use in nanosensors. We have also illustrated that the new integrated sensor NR/Reference NR can be utilized for real-time monitoring of the above studied sources of error during pH-sensing. Furthermore, we have introduced a new surface silanization (using 3-aminopropyltriethoxysilane) method utilizing microwave-assisted heating which compared to conventional heating, yields an amino-terminated monolayer with high surface coverage on the oxide surface of the nanoribbons. A highly uniform and dense monolayer not only reduces the pH sensitivity of the bare-silicon oxide surface in a physiological media but also allows for more receptors to be immobilized on the surface. Protocols for surface functionalization and biomolecule immobilization were evaluated using model systems. Selective spotting of receptor molecules can be used to achieve localized functionalization of individual SiNRs, opening up opportunities for multiplexed detection of analytes.Additionally, we present here a novel approach by integrating droplet-based microfluidics with the SiNR FET sensors. Using the new system we are able to successfully detect trains of droplets with various pH values. The integrated system enables a wide range of label-free biochemical and macromolecule sensing applications based on detection of biological events such as enzyme-substrate interactions within the droplets.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 82 p.
Series
TRITA-ICT, 2016:22
National Category
Nano Technology
Research subject
Information and Communication Technology
Identifiers
URN: urn:nbn:se:kth:diva-191178ISBN: 978-91-7729-075-9OAI: oai:DiVA.org:kth-191178DiVA: diva2:955312
Public defence
2016-09-29, Sal A, Electrum, Kungl Tekniska högskolan, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160825

Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2016-09-19Bibliographically approved
List of papers
1. Effect of microwave-assisted silanization on sensing properties of silicon nanoribbon FETs
Open this publication in new window or tab >>Effect of microwave-assisted silanization on sensing properties of silicon nanoribbon FETs
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2015 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, Vol. 209, 586-595 p.Article in journal (Refereed) Published
Abstract [en]

An important concern with using silicon nanoribbon field-effect transistors (SiNR FET) for ion-sensing is the pH-response of the gate oxide surface. Depending on the application of the FET sensor, this response has to be chemically manipulated. Thus in silicon oxide-gated pH-sensors with integrated sensor and reference FETS, a surface with high pH-sensitivity, compared to the bare gate oxide, is required in the sensor FETs (SEFET), whereas in the reference FETs (REFET) the surface has to be relatively pH-insensitive. In order to control the sensitivity and chemistry of the oxide surface of the nanoribbons, a silanization reagent with a functional group is often self-assembled on the SiNR surface. Choice of a silanization reaction that results in a self-assembled layer on a silicon oxide surface has been studied extensively over the past decades. However, the effect of various self-assembled layers such as monolayers or mixed layers on the electrical response of SiNR FETs in aqueous solution needs to be exploited further, especially for future integrated SEFET/REFET systems. In this work, we have performed a comprehensive study on 3-aminopropyltriethoxysilane (APTES) silanization of silicon oxide surfaces using microwave (MW) heating as a new biocompatible route to conventional methods. A set of complementary surface characterization techniques (ellipsometry, AFM and ATR-FTIR) was used to analyze the properties of the APTES layer deposited on the silicon surface. We have found that a uniform monolayer can be achieved within 10 min by heating the silanization solution to 75 degrees C using MW heating. Furthermore, electrical measurements suggest that little change in device performance is observed after exposure to MW irradiation. Real-time pH measurements indicate that a uniform APTES monolayer not only reduces the pH sensitivity of SiNR FET by passivating the surface silanol groups, but also makes the device less sensitive to cation concentration in the background electrolyte. Our silanization route proves promising for future chemical surface modification of on-chip REFETs.

Keyword
Silicon nanoribbon field-effect transistors, Microwave heating, Silanization, Surface characterization, Electrical measurements, pH sensitivity
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-161089 (URN)10.1016/j.snb.2014.12.030 (DOI)000349082200077 ()2-s2.0-84919754424 (ScopusID)
Funder
VINNOVAKnut and Alice Wallenberg Foundation
Note

QC 20150318

Available from: 2015-03-18 Created: 2015-03-09 Last updated: 2016-08-25Bibliographically approved
2. Hysteresis and Time-delay in the pH Response of Al2O3 and SiO2-gated Silicon Nanoribbon FET Sensors
Open this publication in new window or tab >>Hysteresis and Time-delay in the pH Response of Al2O3 and SiO2-gated Silicon Nanoribbon FET Sensors
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The conventional ion-sensitive field-effect transistor (ISFET) with SiO2 as the insulator of choice has been used as an electrochemical sensor to measure ion concentrations in solutions for many decades. With the ongoing progress in use of silicon nanoribbon (SiNR) FET sensors for fast reliable sensing and the recent demand for pH-sensing technologies in biological applications, it is important to identify the true pH response of the device. However, it has become much more difficult to achieve reliable results across a broad range of pH using SiO2-gated SiNR FET sensors and limitations such as long term drift and hysteresis (also referred to as memory effects) during pH measurements need to be addressed. In this work, we have investigated the electrochemical pH response behavior of silicon oxide-gated SiNR FET sensors and compared it with similar devices (same NR size) but with Al2O3 as the gate oxide. Our studies show that devices passivated with SiO2 show a large hysteresis in the pH response both in acidic and in basic direction, whereas Al2O3 surfaces show slight hysteresis and only in the acidic pH range. Furthermore, in case of SiO2, the total response-time after a pH change appears to be a combination of a fast transient and a slow drift which is related both to the type of oxide and the concentration of the background electrolyte. Consequently, to minimize errors in pH measurements caused by hysteresis and delayed response, we advise performing the measurements at low ionic concentrations and preferably to replace SiO2 by Al2O3 as the gate oxide. In biological applications, we also recommend the integration of an on-chip reference nanoribbon FET for real-time monitoring of problems such as long-term drift and slow response.

National Category
Nano Technology
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-191180 (URN)
External cooperation:
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160825

Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2016-08-25Bibliographically approved
3. Integration of a Droplet-Based Microfluidic System and Silicon Nanoribbon FET Sensor
Open this publication in new window or tab >>Integration of a Droplet-Based Microfluidic System and Silicon Nanoribbon FET Sensor
2016 (English)In: Micromachines, ISSN 2072-666X, E-ISSN 2072-666XArticle in journal (Refereed) Published
Abstract [en]

We present a novel microfluidic system that integrates droplet microfluidics with a silicon nanoribbon field-effect transistor (SiNR FET), and utilize this integrated system to sense differences in pH. The device allows for selective droplet transfer to a continuous water phase, actuated by dielectrophoresis, and subsequent detection of the pH level in the retrieved droplets by SiNR FETs on an electrical sensor chip. The integrated microfluidic system demonstrates a label-free detection method for droplet microfluidics, presenting an alternative to optical fluorescence detection. In this work, we were able to differentiate between droplet trains of one pH-unit difference. The pH-based detection method in our integrated system has the potential to be utilized in the detection of biochemical reactions that induce a pH-shift in the droplets.

Keyword
NanoFET;silicon nanoribbon;droplet microfluidics;pH measurement
National Category
Nano Technology
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-191177 (URN)10.3390/mi7080134 (DOI)
External cooperation:
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160825

Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2016-08-25Bibliographically approved
4. Localized Functionalization and Integration with Microfluidics for Multiplexed Biomolecule Detection using Silicon Nanoribbon-FET Sensors
Open this publication in new window or tab >>Localized Functionalization and Integration with Microfluidics for Multiplexed Biomolecule Detection using Silicon Nanoribbon-FET Sensors
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Biological processes causing different medical conditions are seldom characterized by the simple presence or absence of a single biomarker molecule and it can be expected that biosensors with options for multiplexed detection of a panel of analytes will be required for the development of bed-side diagnostic/prognostic tools for personalized healthcare. One sensor technology with potential to be used for label-free detection of biomolecules is based on Silicon Nanoribbon Field-Effect Transistors (SiNR FET). In this study, the possibilities for multiplexed detection of biomolecules have been explored by the integration of a SiNR FET device with a microfluidic system, in combination with localized immobilization of receptor molecules using a microdispensing instrument. SiNR FET devices were fabricated using CMOS technology and integrated with a microfluidic delivery system composed of channels defined in an SU-8 layer, covered with a PDMS lid. Switching between buffer solutions of different pH was used to demonstrate that the microfluidic system could be used for controlled sample delivery. The shift in conductance of the sensing wire upon change of pH showed that the SiNR FET devices were functional. Protocols for surface functionalization and biomolecule immobilization were evaluated using model systems based on synthetic complementary DNA oligonucleotides and the protein A-derived Z domain and its interaction with immunoglobulin G. The study demonstrates that localized immobilization of biomolecules on silicon nanoribbons can be achieved, opening up for multiplexed detection of analytes and improved possibilities for referencing.

National Category
Engineering and Technology
Research subject
Biotechnology
Identifiers
urn:nbn:se:kth:diva-191181 (URN)
External cooperation:
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160825

Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2016-08-25Bibliographically approved

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