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 the tiniest concentrations of the target molecule in complex biological media, such as blood, without requiring pretreatment of the sample. They provide highly specific information, which can be used as a basis for selecting the appropriate treatment, criminal law measures (e.g. in case of drug offenses) or product safety (e.g. food inspections).

The Working Group on Biomimetic Functional Materials works on developing fast homogeneous tests with an inexpensive electrochemical readout and highly sensitive fluorescence-based assays. We possess special expertise in non-invasive sampling, such as from saliva. Based on our patented ultra-fast redox quenching immunoassay, which takes just 15 seconds, we offer solutions for any protein, peptide and small molecule analytes. We also offer advice here when it comes to the search for antibody producers, the chemical synthesis of bioconjugates and even the concept development for custom 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