zero-mode waveguide
{{Short description|Optical waveguide}}
A zero-mode waveguide is an optical waveguide that guides light energy into a volume that is small in all dimensions compared to the wavelength of the light.
Zero-mode waveguides have been developed for rapid parallel sensing of zeptolitre sample volumes, as applied to gene sequencing, by Pacific Biosciences (previously named Nanofluidics, Inc.)
{{Cite book
| title = DNA sequencing: optimizing the process and analysis
| author = Jan Kieleczawa
| publisher = Jones & Bartlett Publishers
| year = 2004
| isbn = 978-0-7637-4782-4
| page = 190
| url = https://books.google.com/books?id=23NGy0VuVUEC&q=zero-mode-waveguide&pg=PA190
}}
A waveguide operated at frequencies lower than its cutoff frequency (wavelengths longer than its cutoff wavelength) and used as a precision attenuator is also known as a "waveguide below-cutoff attenuator."
{{Cite journal
| doi = 10.1109/22.643852
| author = D. H. Russell
| journal = IEEE Trans. Microwave Theory and Technology
| title = The waveguide below-cutoff attenuation standard
| volume = 45
| issue = 12
| pages = 2408–2413
| date = Dec 1997
|bibcode = 1997ITMTT..45.2408R | s2cid = 6236996
| url = https://zenodo.org/record/1232142
}}
The zero-mode waveguide is made possible by creating circular or rectangular nanoapertures using focused ion beam on an aluminium layer.{{cite journal | last1=Baibakov | first1=Mikhail | last2=Barulin | first2=Aleksandr | last3=Roy | first3=Prithu | last4=Claude | first4=Jean-Benoît | last5=Patra | first5=Satyajit | last6=Wenger | first6=Jérôme | title=Zero-mode waveguides can be made better: fluorescence enhancement with rectangular aluminum nanoapertures from the visible to the deep ultraviolet | journal=Nanoscale Advances | volume=2 | issue=9 | date=1999-02-22 | doi=10.1039/D0NA00366B | pages=4153–4160 | pmid=36132755 | pmc=9417158 | bibcode=2020NanoA...2.4153B | doi-access=free }}
The zero-mode waveguide can also enhance fluorescence signals due to surface plasmons generated at metal-dielectric interfaces.{{Cite journal |last1=Baibakov |first1=Mikhail |last2=Barulin |first2=Aleksandr |last3=Roy |first3=Prithu |last4=Claude |first4=Jean-Benoît |last5=Patra |first5=Satyajit |last6=Wenger |first6=Jérôme |date=2020 |title=Zero-mode waveguides can be made better: fluorescence enhancement with rectangular aluminum nanoapertures from the visible to the deep ultraviolet |journal=Nanoscale Advances |language=en |volume=2 |issue=9 |pages=4153–4160 |doi=10.1039/D0NA00366B|pmid=36132755 |pmc=9417158 |bibcode=2020NanoA...2.4153B }} Due to surface plasmon generation field is localized and enhanced as well as it changes the LDOS inside the cavity which leads to increase in Purcell Factor of analyte molecules inside the zero-mode waveguide{{Cite journal |last1=Barulin |first1=Aleksandr |last2=Roy |first2=Prithu |last3=Claude |first3=Jean-Benoît |last4=Wenger |first4=Jérôme |date=2021-10-21 |title=Purcell radiative rate enhancement of label-free proteins with ultraviolet aluminum plasmonics |url=https://iopscience.iop.org/article/10.1088/1361-6463/ac1627 |journal=Journal of Physics D: Applied Physics |volume=54 |issue=42 |pages=425101 |doi=10.1088/1361-6463/ac1627 |arxiv=2107.06357 |bibcode=2021JPhD...54P5101B |s2cid=235829393 |issn=0022-3727}}
The zero-mode waveguide is very useful for Ultraviolet Auto-fluorescence spectroscopy on tryptophan-carrying proteins like beta-galactosidase.{{cite journal |last1=Barulin |first1=Aleksandr |last2=Claude |first2=Jean-Benoît |last3=Patra |first3=Satyajit |last4=Bonod |first4=Nicolas |last5=Wenger |first5=Jérôme |title=Deep Ultraviolet Plasmonic Enhancement of Single Protein Autofluorescence in Zero-Mode Waveguides |journal=Nano Letters |date=9 October 2019 |volume=19 |issue=10 |pages=7434–7442 |doi=10.1021/acs.nanolett.9b03137|pmid=31526002 |arxiv=1909.08227 |bibcode=2019NanoL..19.7434B |s2cid=202660648 }} With further modification of the zero-mode waveguide with a conical reflector, it is possible to study the dynamic process of smaller proteins like streptavidin with 24 tryptophan.
The modified zero-mode waveguide with a conical reflector can be further optimized to enhance the signal-to-noise ratio and reach the ultimate sensitivity of single tryptophan proteins like TNase.{{cite journal |last1=Roy |first1=Prithu |last2=Claude |first2=Jean-Benoît |last3=Tiwari |first3=Sunny |last4=Barulin |first4=Aleksandr |last5=Wenger |first5=Jérôme |title=Ultraviolet Nanophotonics Enables Autofluorescence Correlation Spectroscopy on Label-Free Proteins with a Single Tryptophan |journal=Nano Letters |date=5 January 2023 |volume=23 |issue=2 |pages=497–504 |doi=10.1021/acs.nanolett.2c03797|pmid=36603115 |arxiv=2301.01516 |bibcode=2023NanoL..23..497R |s2cid=255416119 }}