<p>Canines can detect different diseases simply by smelling different biological sample types, including  urine,  breath  and  sweat.  This  has  led  researchers  to  try  and  discovery  unique  volatile  organic compound (VOC) biomarkers. The power of VOC biomarkers lies in the fact that one day they may be able to be utilized for noninvasive, rapid and accurate diagnostics at a point of care using  miniaturized  biosensors.  However,  the  identity  of  the  specific  VOC  biomarkers  must  be  demonstrated before designing and fabricating sensing systems. Through  an  extensive  series  of  experiments,  VOCs  in  urine  are  profiled  by  solid  phase  microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) to identify biomarkers for breast cancer using murine models. The results from these experiments indicated that  unique  classes  of  urinary  VOCs,  primarily  terpene/terpenoids  and  carbonyls,  are  potential  biomarkers  of  breast  cancer.  Through  implementing  chemometric  approaches,  unique  panels  of  VOCs  were  identified  for  breast  cancer  detection,  identifying  tumor  location,  determining  the  efficacy of dopaminergic antitumor treatments, and tracking cancer progression. Other diseases, including COVID-19 and hypoglycemia (low blood sugar) were also probed to identify volatile biomarkers present in breath samples.  VOC biomarker identification is an important step toward developing portable gas sensors, but  another  hurdle  that  exists  is  that  current  sensors  lack  selectivity  toward  specific  VOCs  of  interest.  Furthermore,  testing  sensors  for  sensitivity  and  selectivity  is  an  extensive  process  as  VOCs  must  be  tested  individually  because  the  sensors  do  not  have  modes  of  chromatographic  separation or compound identification. Another set of experiments is presented to demonstrate that SPME  fibers  can  be  coated  with  materials,  used  to  extract  standard  solutions  of  VOCs,  and  analyzed  by  GC-MS  to  determine  the  performance  of  various  gas  sensing  layers.  In  the  first  of  these  experiments,  polyetherimide  (PEI)  was  coated  onto  a  SPME  fiber  and  compared  to  commercial polyacrylate (PAA) fibers. The second experiment tuned the extraction efficiency of polyvinylidene fluoride (PVDF) - carbon black (CB) composites and showed that they had higher sensitivity  for  urinary  VOC  extraction  relative  to  a  polydimethylsiloxane  (PDMS)  SPME  fiber.  These results demonstrate SPME GC-MS can rapidly characterize and tune the VOC adsorption capabilities of gas sensing layers. </p>