Low Attomole Limit of Quantification on an Orbitrap Fusion Lumos Tribrid Mass Spectrometer

Importance of the topic

The accurate quantification of low-abundance proteins and peptides in complex biological samples remains a major challenge in proteomics. Key targets, including transcription factors and post-translationally modified species, can exist at attomole levels against a background spanning several orders of magnitude. Developing workflows capable of reliable detection, linear quantification, and high reproducibility at these trace levels is essential for biomarker discovery, mechanistic studies, and quality control applications.

Objectives and study overview

This study assessed the limits of quantification (LOQ), dynamic range, and precision of targeted and data-independent acquisition strategies on the Thermo Scientific Orbitrap Fusion Lumos Tribrid mass spectrometer. Stable isotope-labeled peptide standards (PRTC mixture) were spiked into complex HeLa or lung cancer cell digests over a concentration range from 1 attomole to 100 femtomole per microliter. Methods compared included Parallel Reaction Monitoring (PRM), Wide Isolation Selected Ion Monitoring (WiSIM-DIA), classic DIA (cDIA), and Data-Dependent Acquisition (DDA).

Methodology and instrumentation used

• Sample preparation: Heavy Lysine/Arginine-labeled PRTC synthetic peptides spiked into 200 ng HeLa or 1 µg NSCLC digest.
• LC setup: Thermo Easy-nLC 1000 with 75 µm × 50 cm PepMap Easy-Spray column, 300 nL/min flow; gradients of 5–25% B over 120 min + 25–40% B over 35 min for DIA, or 20 min + 8 min for PRM.
• Mass spectrometry: Orbitrap Fusion Lumos Tribrid with high-capacity ion transfer tube and ion funnel.
  • DDA: 120 000 resolution MS1, 30 000 HCD MS2, 3 s cycle.
  • PRM: 0.7 m/z isolation, 60 000 resolution MS2.
  • WiSIM: three 200 m/z SIM windows @240 000 resolution + 17 CID MS2 scans in ion trap.
  • cDIA: sequential 15 m/z windows MS2 @30 000 resolution + 120 000 MS1.
• Data analysis: Proteome Discoverer 2.0 (SEQUEST-HT), Spectronaut, Skyline; 1% FDR, MS1 tolerance ±10 ppm, MS2 tolerance ±0.02 Da (Orbitrap) or 0.6 Da (ion trap).

Main results and discussion

• PRM achieved LOQs down to 1 attomole with CV < 15%, linearity over six orders (R² > 0.99), and average CV < 11% across 55 peptides.
• WiSIM-DIA detected PRTC peptides at 100 attomole in 1 µg matrix using 240 000 resolution SIM, demonstrating confident identification in complex digest.
• cDIA quantified 5964 protein groups (6.9% median CV) from 500 ng HeLa, recovering ~92% of a DDA-derived library; compared with the prior-generation Fusion, the Lumos Tribrid identified up to 30% more proteins and unique peptides at 100/500 ng loads.
• Direct PRM comparison between Fusion Lumos and Fusion showed more fragment ions and higher signal-to-noise on the Lumos at low amol levels due to improved ion transmission and advanced quadrupole technology.

Benefits and practical applications

• Sub-attomole sensitivity supports quantification of extremely low-level biomarkers and regulatory proteins.
• Wide dynamic range workflows enable both discovery and targeted validation in a single platform.
• High reproducibility (CV < 10–20%) and linear response facilitate robust assay development for QA/QC and clinical studies.

Future trends and potential applications

• Pushing LOQs below the attomole threshold through optimized ion optics and acquisition schemes.
• Integration of automated, multiplexed targeted assays for precision medicine and biomarker pipelines.
• Expansion of DIA spectral libraries to deepen proteome coverage in high-throughput studies.
• Hybrid approaches combining PRM and DIA for comprehensive quantification of rare, modified, or low-abundance species.

Conclusion

The Orbitrap Fusion Lumos Tribrid mass spectrometer, leveraging a brighter ion source, advanced quadrupole technology, and versatile acquisition modes, achieves attomole-level quantification with excellent linearity and precision. Both targeted (PRM, WiSIM) and DIA (cDIA) strategies benefit from enhanced sensitivity and dynamic range, underpinning next-generation proteomics applications.

References

• Peterson, A. C. et al. Parallel Reaction Monitoring for High Resolution and High Mass Accuracy Quantitative, Targeted Proteomic. Molecular & Cellular Proteomics, 11, 1475–1488 (2011).
• Kiyonami, R. et al. Large Scale Targeted Protein Quantification Using WiSIM-DIA Workflow on an Orbitrap Fusion Tribrid Mass Spectrometer. Application Note AN64085 (2014).
• Senko, M. et al. Novel Quadrupole/Linear Ion Trap/Orbitrap Tribrid Mass Spectrometer Improving Proteome Coverage and Peptide Identification Rates. Analytical Chemistry, 85(24), 11710–11714 (2013).