###Let's abstract your task to determine dissolved oxygen (DO) to something more general:

1. You have to tie an observable to a concentration.
2. It would be nice if the method would work over a broad range of concentrations.
3. The method should be specific, or, alt least, very selective.
4. If possible, this relation should be linear.
5. It would be nice if the method could be packed into a sensor that works on its own (permanently or in cycles) and does not require a lot of personal interaction (= autonomous probe)

###What properties of molecular oxygen dissolved in water can be measured?

• In water, $\ce{O2}$ can be reduced electrochemically: $\ce{O2 + 4e- + 2 H2O -> 4 OH-}$
  → Have a look for galvanic and polarographic oxygen sensors
• Molecular oxygen is known to quench the luminescence of electronically excited states of dyes. The observed luminescence intensity (and lifetime) is reciprocally proportional to the the concentration of the quencher(Stern-Volmer equation)
  → Have a look for luminescence-based oxygen sensors

Let's abstract your task to determine dissolved oxygen (DO) to something more general:

1. You have to tie an observable to a concentration.
2. It would be nice if the method would work over a broad range of concentrations.
3. The method should be specific, or, alt least, very selective.
4. If possible, this relation should be linear.
5. It would be nice if the method could be packed into a sensor that works on its own (permanently or in cycles) and does not require a lot of personal interaction (= autonomous probe)

What properties of molecular oxygen dissolved in water can be measured?

• In water, $\ce{O2}$ can be reduced electrochemically: $\ce{O2 + 4e- + 2 H2O -> 4 OH-}$
  → Have a look for galvanic and polarographic oxygen sensors
• Molecular oxygen is known to quench the luminescence of electronically excited states of dyes. The observed luminescence intensity (and lifetime) is reciprocally proportional to the the concentration of the quencher(Stern-Volmer equation)
  → Have a look for luminescence-based oxygen sensors

###Let's abstract your task to determine dissolved oxygen (DO) to something more general:

1. You have to tie an observable to a concentration.
2. It would be nice if the method would work over a broad range of concentrations.
3. The method should be specific, or, alt least, very selective.
4. If possible, this relation should be linear.
5. It would be nice if the method could be packed into a sensor that works on its own (permanently or in cycles) and does not require a lot of personal interaction (= autonomous probe)

###What properties of molecular oxygen dissolved in water can be measured?

• In water, $\ce{O2}$ can be reduced electrochemically: $\ce{O2 + 4e- + 2 H2O -> 4 OH-}$
  → Have a look for galvanic and polarographic oxygen sensors
• Molecular oxygen is known to quench the luminescence of electronically excited states of dyes. The observed luminescence intensity (and lifetime) is reciprocally proportional to the the concentration of the quencher(Stern-Volmer equation)
  → Have a look for luminescence-based oxygen sensors

###Let's abstract your task to determine dissolved oxygen (DO) to something more general:

1. You have to tie an observable to a concentration.
2. It would be nice if the method would work over a broad range of concentrations.
3. The method should be specific, or, alt least, very selective.
4. If possible, this relation should be linear.
5. It would be nice if the method could be packed into a sensor that works on its own (permanently or in cycles) and does not require a lot of personal interaction (= autonomous probe)

###What properties of molecular oxygen dissolved in water can be measured?

• In water, $\ce{O2}$ can be reduced electrochemically: $\ce{O2 + 4e- + 2 H2O -> 4 OH-}$
  → Have a look for galvanic and polarographic oxygen sensors
• Molecular oxygen is known to quench the luminescence of electronically excited states of dyes. The observed luminescence intensity (and lifetime) is reciprocally proportional to the the concentration of the quencher(Stern-Volmer equation)
  → Have a look for luminescence-based oxygen sensors