**5.2. Technology for fabrication of nanofluidic channels**

According to the National **S**cience Foundation (NSF) in the US and its National Nanotechnology Initiative (NNI), nanotechnology involves *"the application of scientific knowledge to manipulate and control matter in the nanoscale"* [158, 170], more or less arbitrarily defined at ≤100 nm [158, 170]. Nanofluidics often falls under nano electro mechanical systems (NEMS) [164, 177–179, 184] typically fabricated using complementary metal oxide semiconductor (CMOS) technology [177, 178].

chips (**Figures 11** and **12**). Future developments include coupling of standard CMOS fabrication technology [179, 183, 184, 195–197] with microfluidics or millifluidics, thus allowing integration of fluidics with electronics. Microinstruments are those with at least one critical (or essential) component operating in the micro-regime. For nanofluidics as may be applied to chemical analysis, it appears that it will be best if nanofluidic channels was packaged along-

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It is envisioned that future fluidics (**Figure 1**) will be embedded within portable micro- or nano-instruments for measurements *on-site* (i.e., in the field). Such instruments will have (some) energy autonomy [198–200], will incorporate some *"smarts"* [201] (e.g., based on Artificial Intelligence and Deep Learning) and will have wireless capability [202] so that they can become a part of the **I**nternet **o**f **T**hings (**IoT**) [200–203]. Clearly, fluidics (e.g., milli-, micro- or nano-) have the potential to become critical components of mobile (or even wear-

Financial assistance from NSERC (Natural Sciences and Engineering Research Council) of Canada is gratefully acknowledged. A special thank you to Professor (now Emeritus, ETH Zurich, Switzerland) Dr. Henry Baltes for the many enlightening discussions we had on

able) instruments that are *"cheap, smart and under wireless control"* [139].

Address all correspondence to: vkaranassios@uwaterloo.ca

Department of Chemistry and Waterloo Institute for Nanotechnology,

[1] Bruus H. Theoretical Microfluidics. Oxford, UK: Oxford University Press; 2008

[3] Tabeling P. Introduction to Microfluidics. Oxford, UK: Oxford University Press; 2011

[4] Mitra SK, Chakraborty S, editors. Microfluidics and Nanofluidics. Florida: CRC Press; 2011

[6] Kirby BJ. Micro- and Nano-Scale Fluid Mechanics. Cambridge, UK: Cambridge University

[2] Kumar CS. Microfluidics in Nanotechnology. New York: Wiley; 2010

[5] Madou MJ. Fundamentals of Microfabrication. Florida: CRC Press; 2011

side microfluidic channels.

**Acknowledgements**

MEMS and on miniaturization.

University of Waterloo, Canada

**Author details**

Vassili Karanassios

**References**

Press; 2013

For nanofabrication, many technologies have been described [159–162, 165, 166, 169, 171, 172, 180]. Some of them are nano-specific [159, 169] for example, scanning probe lithography (SPL) [161], etching using a focused ion beam (FIB) [171] and nanoimprinting [159]. In many cases use of a cross-sectional area of a nanochannel is preferred (e.g., 10 nm by 10 nm) rather than aspect ratio. Nanofluidic channels can be nanofabricated using either top-down or bottom-up approaches.

**Top down methods of fabrication of nanochannels:** By analogy to micromachining, these fabrication methods include bulk nanomachining; surface nanomachining; and, imprinting (as is typical of soft-lithography) [159, 161–165, 169]. A top plate is typically used to cover nanochannels but due the nanosize of the channels and unless precautions are taken, channels may plug-up during bonding.

**Bottom up methods of nanostructure formation:** in some cases molecules can be "convinced" to self-assemble into nanostructures by controlling chemical conditions [160, 162].

**Associated nanofabrication technologies** include scanning probe lithography (**SPL**) [161], electron beam lithography (EBL) [159] and dip-pen nanolithography [185]. Such approaches are typically used to bypass the diffraction-limit of photolithography or to provide new capabilities.
