Gravity-Driven Microfluidic Siphons: Fluidic Characterization and Application to Quantitative Immunoassays

Nuno M Reis, Sarah H Needs, Sophie M Jegouic, Kirandeep K Gill, Sirintra Sirivisoot, Scott Howard, Jack Kempe, Shaan Bola, Kareem Al-Hakeem, Ian M Jones, Tanapan Prommool, Prasit Luangaram, Panisadee Avirutnan, Chunya Puttikhunt, Alexander D Edwards

Research output: Contribution to journalArticlepeer-review

17 Citations (SciVal)


A range of biosensing techniques including immunoassays are routinely used for quantitation of analytes in biological samples and available in a range of formats, from centralized lab testing (e.g., microplate enzyme-linked immunosorbent assay (ELISA)) to automated point-of-care (POC) and lateral flow immunochromatographic tests. High analytical performance is intrinsically linked to the use of a sequence of reagent and washing steps, yet this is extremely challenging to deliver at the POC without a high level of fluidic control involving, e.g., automation, fluidic pumping, or manual fluid handling/pipetting. Here we introduce a microfluidic siphon concept that conceptualizes a multistep ″dipstick″ for quantitative, enzymatically amplified immunoassays using a strip of microporous or microbored material. We demonstrated that gravity-driven siphon flow can be realized in single-bore glass capillaries, a multibored microcapillary film, and a glass fiber porous membrane. In contrast to other POC devices proposed to date, the operation of the siphon is only dependent on the hydrostatic liquid pressure (gravity) and not capillary forces, and the unique stepwise approach to the delivery of the sample and immunoassay reagents results in zero dead volume in the device, no reagent overlap or carryover, and full start/stop fluid control. We demonstrated applications of a 10-bore microfluidic siphon as a portable ELISA system without compromised quantitative capabilities in two global diagnostic applications: (1) a four-plex sandwich ELISA for rapid smartphone dengue serotype identification by serotype-specific dengue virus NS1 antigen detection, relevant for acute dengue fever diagnosis, and (2) quantitation of anti-SARS-CoV-2 IgG and IgM titers in spiked serum samples. Diagnostic siphons provide the opportunity for high-performance immunoassay testing outside sophisticated laboratories, meeting the rapidly changing global clinical and public health needs.

Original languageEnglish
Pages (from-to)4338-4348
Number of pages11
JournalACS Sensors
Issue number12
Early online date2 Dec 2021
Publication statusPublished - 24 Dec 2021

Bibliographical note

Funding Information:
The authors are grateful to Patrick Hester and David Gough from Lamina Dielectrics Ltd. for assistance with the development of the siphon cassettes used for dengue and NS1 diagnostics. K.K.G. is grateful to EPSRC and the University of Bath for funding of a PhD scholarship. This work was partially supported by a Wellcome Trust Pathfinder award (reference 204388/Z/16/Z), a Newton Fund Institutional Links award (reference IL35237556), EPSRC (grant EP/R022410/1), and Defence and Security Accelerator (contract reference ACC6010011).


  • biosensor
  • dengue NS1
  • immunoassays
  • microfluidic
  • porous membrane
  • portable ELISA
  • siphon
  • smartphone diagnostics

ASJC Scopus subject areas

  • Bioengineering
  • Instrumentation
  • Process Chemistry and Technology
  • Fluid Flow and Transfer Processes


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