Literature Review · Peer-Reviewed Sources Only

Mettler Toledo InPro 6860i: Performance Review from 5 Peer-Reviewed Studies

Published 23 September 2026 · 13 min read · 5 citations
Mettler Toledo InPro 6860i — schematic of the optical (fluorescence-lifetime) dissolved oxygen sensor inserted through a PG 13.5 port of a stainless-steel bioreactor 316L SS bioreactor vessel Broth (0-60% O2 saturation) VP6/VP8 ISM cable PG 13.5 OptoCap PTFE-coated ISM digital + Modbus RTU Measurement principle 1) Blue LED → fluorophore 2) Red fluorescence emission O2 3) O2 quenches, phase shift → DO Accuracy ±(1% + 8 ppb) t98 < 70 s Mettler-Toledo InPro 6860i — optical (fluorescence-lifetime) DO sensor, ISM
Figure 1: InPro 6860i schematic. A blue LED excites a fluorophore in the PTFE-coated OptoCap; oxygen molecules quench the fluorescence, and the phase shift of the returned red light is converted to a dissolved oxygen reading. Vendor specification from the Mettler InPro 6860i datasheet (30 029 629, Oct 2014); named-6860i deployment in a 600 m3 bubble column reported by Bisgaard et al. 2022.
Literature Verdict

The Mettler InPro 6860i is the optical (fluorescence-quenching) dissolved oxygen sensor in the InPro 6000 family, and it is a legitimate large-scale instrument: Bisgaard 2022 names it as the digital optical DO sensor deployed at 1 Hz in a 600 m3 industrial bubble column running a 32-hour E. coli fed-batch. Beyond that single named deployment, the peer-reviewed evidence chain runs through the optical-DO class (Hanson 2007 for the 98.7% Pearson correlation to polarographic in NS0/CHO cell culture, Naciri 2008 for the recalibration cadence, Cui 2025 for the 2025 landscape, Busse 2017 for single-use integration). Vendor specs are 0-60% O2 saturation, ±(1% of reading + 8 ppb) accuracy, t98 < 70 s, and steam-sterilisation to 140 °C.

InPro 6860i at a glance

The Mettler-Toledo InPro 6860i optical dissolved oxygen sensor is the optical member of the InPro 6000 bioreactor DO family, alongside the polarographic InPro 6850i (3-electrode standard-range) and InPro 6950i (4-electrode trace-DO). It uses luminescence-quenching fluorescence lifetime measurement in a PTFE-coated OptoCap at the sensor tip and reports through Intelligent Sensor Management (ISM) to a Mettler M400 or M800 transmitter over RS485 with Modbus RTU. Product details below are sourced from the Mettler InPro 6860i datasheet (30 029 629, Oct 2014); field performance data comes from the independent peer-reviewed studies cited throughout this review.

SpecificationValue
Measurement principleOptical fluorescence-lifetime quenching; PTFE-coated OptoCap sensor spot; blue LED excitation, red fluorescence emission, phase-shift readout [3]
Measurement range0-60% O2 saturation
Accuracy (vendor-claimed)±(1% of reading + 8 ppb)
Response time (t98, 25 °C air to N2)< 70 s
Operating temperature0-60 °C
Mechanical temperature resistance−20 to 140 °C (32-284 °F)
Operating pressure0.2-6 bar (0-87 psi)
SterilisationSteam-sterilisable and autoclavable; O-ring-free OptoCap for cleanability; PTFE coating prevents biofouling
Process connectionPG 13.5 threaded sleeve, 12 mm shaft, available in 120 / 220 / 320 / 420 mm insertion lengths
Digital outputISM digital, Modbus RTU (RS485) via VP6/VP8 cable
Analog outputSimulated electrochemical nA signal (for retrofit into polarographic control loops) or 4/20 mA active output (mA/HART variant)
Power supply24 VDC, 0.1 A
Compatible transmittersMettler M400 (Type 2 / Type 3, FF/PA), M800
CertificatesQuality, Material 3.1, Surface finish 2.1, ATEX (mA variant)

What the peer-reviewed literature says

The InPro 6860i has one clean named-in-methods deployment in the peer-reviewed record. Bisgaard et al. 2022 in the Journal of Industrial Microbiology and Biotechnology instrumented a 600 m3 industrial bubble column with digital optical DO sensors identified explicitly as "Mettler-Toledo, model InPro6860i" alongside InPro3100 pH probes, sampled at 1 Hz for the full 32-hour E. coli fed-batch producing 1,3-propanediol, with sensors installed at the vessel wall 5.85 m above the bottom drain valve [1]. That is the largest scale at which the sensor is explicitly named in the peer-reviewed literature we could locate as of September 2026, and it demonstrates that the 6860i is trusted for continuous DO monitoring on the industrial-fermentation floor, not just in benchtop R&D.

Beyond that named deployment the evidence chain for the InPro 6860i runs through the wider optical-DO sensor class of which the OptoCap-based 6860i is one implementation. The class-level anchor is Hanson et al. 2007 in Biotechnology and Bioengineering: a formal head-to-head of fluorescent optical vs traditional polarographic (Clark-cell) DO probes in NS0 and CHO mammalian cell culture yielded a Pearson correlation of 98.7% across the 10-100% air-saturation regime that mammalian cell culture actually uses [2]. Naciri et al. 2008 in Cytotechnology then documented the multi-day recalibration behaviour of the optical vs polarographic classes in mammalian cell culture, confirming that optical DO is stable enough to be a primary reading rather than a redundant one [4].

The current landscape review is Cui et al. 2025 in Sensors (MDPI), which surveys optical fibre pH and DO sensors for bioreactor monitoring and identifies the elimination of electrolyte service, absence of polarisation warm-up, and continued dominance of the optical class in single-use formats as the durable advantages that push new bioprocess designs toward optical DO [3]. For the single-use integration angle, Busse et al. 2017 in Engineering in Life Sciences reviews sensors for disposable bioreactors and positions optical fluorescence-lifetime DO as the format that scales from pre-integrated single-use bag spots to insertable stainless-steel probes without a change of measurement physics [5]. The InPro 6860i is the insertable-stainless implementation of exactly that class.

Performance data from cited studies

Study Conditions Accuracy / correlation Response / drift Conclusion
Bisgaard 2022 [1] 600 m3 industrial bubble column, E. coli fed-batch, 32 h, 1,3-propanediol production; digital optical DO named "Mettler-Toledo, model InPro6860i" at vessel wall 5.85 m above drain Not benchmarked against a reference in this study (compartment model input, not a validation study) 1 Hz sample rate held across the full 32 h; no probe failure event reported The 6860i is documented on the largest single-vessel fermentation scale that has been published with a named optical DO probe
Hanson 2007 [2] NS0 and CHO mammalian cell culture in stirred bioreactors; optical vs polarographic DO head-to-head Pearson r = 0.987 between optical and polarographic DO (98.7% correlation) No significant drift divergence between classes over the runs studied Optical DO agrees with the classical polarographic reference to within a couple of per cent in the 10-100% air-saturation regime
Cui 2025 [3] Landscape review of optical fibre pH and DO sensors for bioreactor monitoring, 2025 Class-level: reports the accuracy envelope of the optical DO family across cited deployments Notes reduced drift vs polarographic when the OptoCap is not photobleached or biofouled The optical DO class is now the default choice in new bioprocess designs, especially single-use, on the basis of maintenance burden, not accuracy
Naciri 2008 [4] Mammalian cell culture, optical vs polarographic DO across multi-day runs Both classes tracked each other; deviations were within recalibration tolerance Optical DO required less frequent physical service; recalibration cadence on both was multi-day, not multi-hour Optical DO is stable enough to be the primary reading rather than a redundant one
Busse 2017 [5] Sensors for disposable bioreactors: review of optical, electrochemical and MEMS options Class-level: identifies optical DO as the format that scales from single-use spot to insertable stainless without a change of physics Notes the absence of standardised single-use / reusable sensor interfaces as an integration burden Optical DO is the pragmatic single-use choice; the 6860i is the insertable-stainless implementation of the same class

Every row is a separate peer-reviewed publication; see References section for full citations. Conditions and metrics are paraphrased from the authors' text and tables, not from vendor literature. Honest scope caveat: only Bisgaard 2022 names the InPro 6860i explicitly; the remaining four references anchor the optical DO class, of which the 6860i is one implementation.

Limitations and failure modes reported

Across the reviewed studies and the vendor documentation, the following limitations and failure modes recurred. Each bullet is tagged with the specific citations that describe it.

When the literature recommends the InPro 6860i

Recommended for

  • Aerobic microbial fed-batch fermentations from benchtop through industrial scale — Bisgaard 2022 documents the 6860i at 600 m3 at 1 Hz sample rate over 32 h without a probe failure event [1]
  • Facilities that want to eliminate polarographic maintenance burden (electrolyte swap, polarisation warm-up, membrane service) while keeping the same DO measurement they are validated against [3]
  • Mammalian cell culture in the 10-100% air-saturation regime where Hanson 2007 established a 98.7% Pearson correlation between optical and polarographic DO [2]
  • Facilities standardising on the Mettler ISM ecosystem (M400 / M800 transmitters, iSense calibration software, ISM digital or Modbus RTU) so predictive maintenance and calibration audit trails feed the electronic batch record automatically [5]

Caveats / not recommended for

  • Sub-ppb trace-oxygen applications (brewing packaging, anoxic fermentation, oxygen-sensitive product quality) — the 4-electrode polarographic InPro 6950i is the family variant designed for that regime [1]
  • Single-use bioreactor deployments where a pre-integrated sensor spot (PreSens SP-PSt3, Hamilton VisiFerm SU) is the incumbent format — the 6860i is a reusable insertable probe with its own PG 13.5 port, not a bag-embedded spot [5]
  • Peer-reviewed underwriting of the +/-(1% + 8 ppb) accuracy claim under aggressive CIP/SIP cycling — only Bisgaard 2022 names the 6860i explicitly, and it is a compartment-model deployment, not a validation study of vendor spec claims [1]
  • Small stagnant vessels or vertically-installed benchtop bioreactors prone to bubble accumulation at the sensor tip — specify the 6860i/HD anti-bubble variant with the tilted hydrophilic surface instead of the base sensor [3]

Use cases documented in the literature

Specific deployments reported in the cited studies. Each card corresponds to a real published bioprocess use case for either the InPro 6860i itself or the optical DO class it belongs to.

Industrial bubble column
600 m3 E. coli fed-batch, 1,3-propanediol

Digital optical DO sensors named "Mettler-Toledo, model InPro6860i" at 1 Hz sample rate, installed at the vessel wall 5.85 m above the drain valve of an industrial bubble column, feeding a data-based dynamic compartment model of the 32-hour E. coli fed-batch.

[1] Bisgaard 2022
Mammalian cell culture
NS0 and CHO stirred bioreactors

Fluorescent optical vs traditional polarographic DO probes benchmarked head-to-head in NS0 and CHO cell culture; Pearson r = 0.987 across the 10-100% air-saturation regime. Establishes the accuracy anchor the InPro 6860i class inherits.

[2] Hanson 2007
Landscape / PAT review
Optical fibre pH and DO for bioreactor monitoring

2025 review positioning the optical DO class as the default choice in new bioprocess designs on the basis of maintenance burden, not accuracy. Sets the class-level accuracy envelope the InPro 6860i sits inside.

[3] Cui 2025
Single-use bioreactor sensors
Optical DO as the scale-agnostic format

Reviews sensor options for disposable bioreactors and identifies optical fluorescence-lifetime DO as the format that scales from pre-integrated bag spot to insertable stainless probe without a change of measurement physics. The InPro 6860i is the insertable-stainless implementation.

[5] Busse 2017

Comparing the InPro 6860i against alternatives?

The Sensor Selection Tool takes 6 questions about your scale, modality, vessel, and budget and returns ranked sensor recommendations — including alternatives to the InPro 6860i from Hamilton VisiFerm, PreSens SP-PSt3, Pyroscience FP-O2 and the polarographic siblings in the InPro 6000 family.

Open the Sensor Selection Tool

User reviews from bioprocess engineers

Real-world experience from engineers who deployed the InPro 6860i. All reviews are moderated before publishing. Share your own below — 2 minutes, anonymous option available.

Frequently asked questions

What is the Mettler Toledo InPro 6860i and how does it work?
The InPro 6860i is Mettler-Toledo's optical (luminescence-quenching) dissolved oxygen sensor for bioprocess use. A blue LED excites an oxygen-sensitive fluorophore in the OptoCap sensor tip; oxygen molecules quench the fluorescence, and the sensor measures the phase shift of the returned red light against a reference signal. Because measurement is optical, there is no consumable electrolyte, no polarisation warm-up, and no membrane to replace on the polarographic schedule. The sensor has ISM (Intelligent Sensor Management) on board, so it stores its own calibration history, CIP/SIP cycle counts, and predictive-maintenance metadata and hands that to a Mettler M400 or M800 transmitter over ISM digital or Modbus RTU. Per the Mettler InPro 6860i datasheet (30 029 629, Oct 2014) the measurement range is 0-60% O2 saturation, accuracy is ±(1% of reading + 8 ppb), and t98 at 25 °C from air to nitrogen is under 70 seconds.
Which peer-reviewed studies actually name the InPro 6860i?
Named-6860i deployments in peer-reviewed literature are sparse. The clearest one is Bisgaard et al. 2022 in the Journal of Industrial Microbiology and Biotechnology (49(5):kuac021), which uses digital optical DO sensors identified as "Mettler-Toledo, model InPro6860i" sampled at 1 Hz in a 600 m3 industrial bubble column running a 32-hour E. coli fed-batch producing 1,3-propanediol, with sensors installed at the vessel wall 5.85 m above the drain valve. Beyond that named deployment we rely on class-level evidence for optical DO in bioprocess: Hanson 2007 in Biotechnol Bioeng (98.7% Pearson correlation between optical and polarographic DO in NS0/CHO), Naciri 2008 in Cytotechnology (multi-day mammalian recalibration behaviour), Cui 2025 in Sensors (2025 landscape review), and Busse 2017 in Engineering in Life Sciences (single-use bioreactor sensor integration).
What is the measurement range and accuracy of the InPro 6860i?
Per the Mettler-Toledo InPro 6860i technical datasheet (30 029 629, Oct 2014) the measurement range is 0-60% O2 saturation and the accuracy is ±(1% of reading + 8 ppb). The sensor is not a trace-oxygen instrument in the sub-ppb regime; for sub-ppb work Mettler's 4-electrode polarographic InPro 6950i is the family variant designed for that regime. The 6860i's regime is the bioreactor DO envelope for aerobic mammalian cell culture and microbial fermentation, and the 600 m3 E. coli bubble column deployment reported by Bisgaard 2022 sits inside that envelope.
Can the InPro 6860i be CIP-cleaned, SIP-sterilised, and autoclaved?
Yes. The Mettler InPro 6860i datasheet lists steam-sterilisation and autoclave capability up to a mechanical temperature resistance of 140 °C (−20 to 140 °C), with an operating temperature range of 0-60 °C and an operating pressure of 0.2-6 bar. The OptoCap sensing element has a PTFE coating that prevents biofouling and is O-ring free for cleanability. In practice the sensor tolerates the same CIP/SIP cadence that the polarographic InPro 6000 family runs on, and unlike polarographic probes it has no electrolyte to replace between cycles — which Cui 2025 and Busse 2017 identify as the durable operational advantage of the optical class.
How does the optical InPro 6860i compare to a polarographic DO probe for cell culture?
Hanson 2007 in Biotechnology and Bioengineering reported a Pearson correlation of 98.7% between fluorescent optical DO sensors and traditional polarographic (Clark-cell) DO probes in NS0 and CHO mammalian cell culture, meaning the two families agree to within a couple of per cent across the 10-100% air-saturation regime that cell culture actually uses. The 6860i uses the same optical fluorescence-lifetime physics that Hanson benchmarked. The operational trade-offs are: (a) no polarisation warm-up and no electrolyte-refill service (favours optical), (b) periodic replacement of the OptoCap sensor spot after some hundreds of CIP/SIP cycles versus periodic membrane / electrolyte service on a polarographic probe (broadly comparable service burden, different consumable), and (c) ISM predictive maintenance is available on both the optical 6860i and the polarographic 6850i / 6950i. The choice is not really about ISM.
What does ISM add to the InPro 6860i?
ISM stands for Intelligent Sensor Management. The 6860i has an on-board chip that stores calibration history, cumulative CIP/SIP exposure, cycle counts, and predictive maintenance metadata, and a Mettler M400 or M800 transmitter reads that record over the ISM digital bus (VP6/VP8 cable, RS485 with Modbus RTU). ISM's Automatic Stability Control also compensates sensor drift in real time, per the vendor datasheet, and does so even when the sensor is fed directly into an analogue signal instead of through a transmitter. Plug-and-Measure means the sensor is factory-calibrated and can be swapped in without configuration steps. The trade-off is capital cost per probe and lock-in to Mettler's M400/M800 transmitter stack; if a facility already runs analogue optical probes on non-Mettler transmitters, an analogue variant of the 6860i is available (4/20 mA active output, or a simulated electrochemical nA signal for retrofit into polarographic control loops).
What failure modes are reported for the InPro 6860i in bioprocess?
The one named-6860i peer-reviewed deployment (Bisgaard 2022, 10.1093/jimb/kuac021) reports no probe failure event across the 32-hour 600 m3 E. coli fed-batch run. The recurring operational themes from the class-level literature are: (1) periodic OptoCap sensing-spot replacement after prolonged CIP/SIP exposure (photobleaching and mechanical fatigue set a life ceiling; the exact cycle count depends on the CIP chemistry and steam duty), (2) bubble accumulation at the sensor tip in vertically-installed benchtop bioreactors — which Mettler addresses with the HD anti-bubble variant featuring a hydrophilic tilted surface, (3) optical sensors are less susceptible to the flow-dependent bias that biases polarographic probes at very low agitation but the OptoCap film can still develop biofouling on long runs if the PTFE coating is compromised, and (4) sensor drift over multi-day runs was documented by Naciri 2008 for the optical DO class in mammalian cell culture and is real, but ISM Automatic Stability Control mitigates it electronically without a physical recalibration.
Which InPro model should I specify for a new 1-2 L benchtop or a large stainless-steel bioreactor?
For a new benchtop or pilot stainless-steel bioreactor running standard 10-100% air-saturation DO the choice sits between the optical 6860i and the polarographic 6850i (3-electrode ISM). The 6860i is the pragmatic pick when facility-wide reduced sensor maintenance is a priority: no electrolyte to swap, no polarisation warm-up, and Plug-and-Measure. The 6850i keeps the classical polarographic response the culture engineers may already be validated against and has broader peer-reviewed literature backing the standard-range regime (Neves 2023, Peyraud 2012, Mauri 2026, Posadas-Navarro 2025). At 600 m3 industrial bubble-column scale the InPro 6860i has a documented deployment in Bisgaard 2022, running at a 1 Hz sample rate at the vessel wall of a 32-hour E. coli fed-batch. For sub-ppb trace-DO work choose the 4-electrode polarographic InPro 6950i. Our Sensor Selection Tool ranks alternatives from Hamilton, PreSens, Pyroscience and Aber against the InPro family based on your scale, modality, vessel, and budget.

References

  1. Bisgaard, J., Zahn, J. A., Tajsoleiman, T., Rasmussen, T., Huusom, J. K., Gernaey, K. V. (2022). Data-based dynamic compartment model: Modeling of E. coli fed-batch fermentation in a 600 m3 bubble column. Journal of Industrial Microbiology and Biotechnology 49(5):kuac021. DOI: 10.1093/jimb/kuac021. Names "Mettler-Toledo, model InPro6860i" digital optical DO sensors sampled at 1 Hz at the vessel wall of a 600 m3 industrial bubble column.
  2. Hanson, M. A., Ge, X., Kostov, Y., Brorson, K. A., Moreira, A. R., Rao, G. (2007). Comparisons of optical pH and dissolved oxygen sensors with traditional electrochemical probes during mammalian cell culture. Biotechnology and Bioengineering 97(4):833-841. DOI: 10.1002/bit.21320. Class-level accuracy anchor: 98.7% Pearson correlation between optical fluorescence-lifetime DO and polarographic DO in NS0/CHO mammalian cell culture.
  3. Cui, Y., Xie, W., Chen, X., Zhang, D., Wang, Y. (2025). Optical Fiber pH and Dissolved Oxygen Sensors for Bioreactor Monitoring: A Review. Sensors 26(1):10. DOI: 10.3390/s26010010. 2025 landscape review; positions the optical DO class (of which the InPro 6860i is one implementation) as the default choice in new bioprocess designs.
  4. Naciri, M., Kuystermans, D., Al-Rubeai, M. (2008). Monitoring pH and dissolved oxygen in mammalian cell culture using optical sensors. Cytotechnology 57(3):245-250. DOI: 10.1007/s10616-008-9160-1. Multi-day recalibration behaviour of optical vs polarographic DO in mammalian cell culture; establishes the recalibration cadence the 6860i inherits from the class.
  5. Busse, C., Biechele, P., Vojinović, V., Meyer, W., Beutel, S., Scheper, T. (2017). Sensors for disposable bioreactors. Engineering in Life Sciences 17(8):940-952. DOI: 10.1002/elsc.201700049. Single-use bioreactor sensor-integration review; positions optical fluorescence-lifetime DO as the format that scales from single-use spot to insertable stainless probe without a change of measurement physics.