Fluorescence Sensing

Fluorescence (sometimes called photoluminescence)

CHEMISTRY and LIGHT

The emission of light from a chemical, when it is irradiated with light of a different energy:

Substance ABSORBS energy from LIGHT – ‘excited’

Energy is released as LIGHT emission = fluorescence

Practical Experiment:

AIM: To make a selection of fluorescent solutions, and a molecular fluorescence pH sensor

ATTENTION: wear safety goggles – we are going to use ethanol

You will need:BeakerFilter paperFunnelConical flasksSpatulaEthanolWater1 M HCl solution1 M NaOH solution

ACTIVITY

We are going to extract fluorescent molecules from some common items that you may come across at home:

Equipment for the extraction

DISSOLVE the fluorescent compound in a SOLVENT, in a beaker, to form a SOLUTION.

FITLER this solution to remove the RESIDUE, and collect the FILTRATE:

Make up a fluorescent solution of vitamin B2 and another solution of your choice:

1. Make up a fluorescent solution of riboflavin (vitamin B2):- Empty a capsule of vitamin B2 into a beaker, with and dissolve it in 50 mL of

water, and stir- Pour the mixture into a filter funnel, and collect the liquid in the funnel at the

bottom- Use a pipette to collect some of this liquid into a sample vial, put the lid on it,

and look at this under the UV lightWhat light is it absorbing?What type of light is it emitting?

2. Make up a fluorescent solution of optical brightener:- Take a teaspoon of washing powder, and dissolve it in 50 mL of water- Pour the mixture into a filter funnel, and collect the liquid in the funnel at the

bottom- Use a pipette to collect some of this liquid into a sample vial, put the lid on it,

and look at this under the UV lightWhat light is it absorbing?What type of light is it emitting?

2. Or Make up a fluorescent solution of chlorophyll:- Take a handful of spinach leaves, put into sample bag- Add 25 mL of ethanol- Scrunch the leaves in the bag and in the ethanol for a few minutes- Pour the mixture into a filter funnel, and collect the green liquid in the funnel at

the bottom- Use a pipette to collect some of this liquid into a sample vial, put the lid on it,

and look at this under the UV lightWhat light is it absorbing?

What type of light is it emitting?

2. Or Make up a fluorescent solution of curcumin:- Take a teaspoon of turmeric, and dissolve it in 50 mL of ethanol- Pour the mixture into a filter funnel, and collect the liquid in the funnel at the

bottom- Use a pipette to collect some of this liquid into a sample vial, put the lid on it,

and look at this under the UV lightWhat light is it absorbing?What type of light is it emitting?

3. Sensing acidity and basicity:

Take some of your riboflavin (vitamin B2) solution in a plastic vial. Look at the fluorescence under a UV lamp – now change the pH of the solution by adding a few drops of 1M NaOH(aq) solution – compare the fluorescence

You can neutralise the solution with HCl (aq) solution, and then take the solution down to low pH – compare the fluorescence again.

Water is ________________ and has a pH of _______________

Riboflavin (vitamin B2) is _____________ fluorescent in water

NaOH (aq) is _______________ and has a ______________ pH

Riboflavin (vitamin B2) is ______________ fluorescent when NaOH(aq) is added

How can this be reversed, after you have added NaOH(aq)?

The acidity/basicity of a solution can be SENSED with riboflavin (vitmin B2), and we can see whether the solution is neutral or basic by how BRIGHTLY the molecule fluoresces.