Homogeneous immunoassays

Competitive redox quenching immunoassay
© Fraunhofer IZI-BB
Competitive redox quenching immunoassay, taking the example of the pregnancy hormone hCG (schematic). The hCG level in the urine continuously increases after conception (fertilization of the egg). A sample lacking hCG (i.e. not pregnant) triggers a high current signal (green). A sample containing hCG (i.e. successful conception) triggers a lower current signal (red). The signal change takes just 15-20 seconds.

Immunoassays detect lowest concentrations of the target molecule in complex biological media like blood without sample pretreatment. This specific information is often the basis for decisions regarding the correct therapy, criminal law measures (e.g. drug offences) or product safety (e.g. food controls).


The »Biomimetic Functional Materials« group develops rapid homogeneous tests with inexpensive electrochemical readout and highly sensitive fluorescence-based assays. Our know-how are on-invasively obtained samples, especially saliva. Based on our patented ultra-fast redox quenching immunoassay with an assay duration of only 15 seconds, we offer developments for any protein, peptide and small molecule analyte. In this respect, we also offer further consulting in the search for antibody producers, the chemical synthesis of bioconjugates, up to the development of concepts for customized sampling modules, disposables and readout systems.

Measurement signal (nA) of the competitive hCG redox quenching immunoassay
© Fraunhofer IZI-BB
Measurement signal (nA) of the competitive hCG redox quenching immunoassay
  • Steroid detection in saliva
  • HbA1c serum testing


  • Electrochemical process with video microscopy
  • Synthesis and purification of ferrocene conjugates
  • Dry reagent formulation



  • Electrochemical workstation
  • High-speed video microscopy
  • Pilot-scale freeze dryer


  • Tan C, Schenk JA, Gajovic-Eichelmann N, Sellrie F, Bier FF. A new one-step antigen heterologous homogeneous fluorescence immunoassay for progesterone detection in serum. Talanta (2015);134: S. 508-13
  • Uyen Nguyen Hoang Phuong, Nenad Gajovic-Eichelmann, Frank. F. Bier, Thanh Ngo Vo Ke A novel method of immobilizing antigens on gold electrode for immunosensing. Communications in Physics (2015), 25, S. 173-182
  • Ettlinger J, Schenk JA, Micheel B, Ehrentreich-Förster E, Gajovic-Eichelmann N. A Direct competitive homogeneous immunoassay for progesterone – the redox quenching immunoassay. Electroanalysis (2012), 24, S. 1567-1575
  • Tan C, Gajovic-Eichelmann N, Polzius R, Hildebrandt N, Bier FF. Direct detection of Δ9-tetrahydrocannabinol in aqueous samples using a homogeneous increasing fluorescence immunoassay (HiFi). Anal Bioanal Chem (2010), 398, S.2133–2140