MEMS-Based Selective Preconcentration of Trace Level Breath Analytes

This paper presents high-performance micropreconcentrators (muPCs) aimed at breath analysis and a method for eliminating unwanted species from breath samples by using a two-step preconcentration procedure. The muPC consists of embedded high aspect-ratio three-dimensional (3-D) micro pillars coated with an adsorbent polymer. The silicon-glass die has outer dimensions of 7 mm times 7 mm, total inner surface area of ~ 10 m², and a total inner volume of ~ 6.5 muL. The muPC has on-chip thermal desorption capability and comprises more than 3500 micro pillars with dimensions of 30 mum times 120 mum times 240 mum. The preconcentration factor of the presented muPCs was measured to be above 10 000. Results showed the possibility of selective preconcentration by cascading multiple muPCs with temperature and flow control. The work presented here has profound implications for handheld point-of-care breath analysis instrumentation by first concentrating trace levels of VOCs found in human breath undergoing anesthesia such as n-decane (C₁₀), n-dodecane (C₁₂), 2,6-diisopropylphenol (Propofol), n-tetradecane (C₁₄), and n-hexadecane (C₁₆). Second, it succeeded in eliminating water-like solvent (1-propanol) from the sample to be analyzed. Third, it selectively preconcentrated target compound such as Propofol which is used for medical procedures. The relative concentration of Propofol to C₁₄ was changed from 50% (with one muPC ) to 99.8% (with cascaded muPC). The water-like solvent was also eliminated by 99.9%.