Dip a strip,
it changes color.
How?
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The full narration of the video.
Dip a strip of paper in urine, and it can tell whether there's sugar in it. How? At a checkup, a nurse dips a thin strip into the cup. A dozen seconds later, a row of little squares has changed color, some going green, some going purple. Let's start from those colors and work backward.
Zoom in on one square. It isn't plain paper. It's soaked with a ready-made mix of chemicals, then dried, and left to wait. While it's dry, the chemicals can't reach each other, so nothing happens. The moment urine touches it, the water dissolves them, and things get going. The sugar square is like a door that only opens for one key.
The lock only fits the shape of sugar. Salt, water, anything else just won't go in. Once sugar slips in, the lock turns, and switches on a lamp behind the door: a colorless dye turns green. More sugar in the urine means more doors open, more lamps lit, and a deeper color.
That's why the box has a color chart, light to dark. Hold the strip up to it, and the closest match gives you a rough amount. The lock's real name is glucose oxidase, a protein that grabs only glucose. The lamp is called a chromogen, a color-making dye. The urine glucose line on your checkup report comes from this pair. A single strip carries about ten squares, each with a different lock. One catches protein, one catches blood, one catches traces left by bacteria.
But one square has no lock at all. It only checks whether urine is acidic or alkaline. Its dye changes color on its own as acidity changes. Acidic stays orange; the more alkaline, the more it drifts to blue-green. Pool and aquarium strips work the same way: every square hides one chemical, waiting for water.
Still, a strip is only a quick first look. Lots of vitamin C can keep the sugar square from changing. For what a result means, ask a doctor. Something that changes color with acidity is already in your kitchen. Chop some red cabbage and steep it in hot water until it turns purple. Pour two glasses. Add vinegar to one, baking soda to the other. Before you try, take a guess: what color does the vinegar glass turn?
That row of little squares
At a checkup, a nurse dips a thin strip into the cup. A dozen seconds later, a row of little squares has changed color.
Each square only recognizes one thing.
Dry chemicals,
waiting for water
Zoom in on one square. It isn't plain paper. It's soaked with a ready-made mix of chemicals, then dried.
While it's dry, the chemicals can't reach each other, so nothing happens. The moment urine touches it, the water dissolves them and the reaction starts.
A lock that only fits sugar
The sugar square is like a door that only opens for one key. The lock only fits the shape of sugar. Salt and water won't go in.
Once sugar slips in, the lock turns and switches on a lamp behind the door: a colorless dye turns green.
The lock's real name is glucose oxidase, a protein that grabs only glucose. It turns the sugar into a little hydrogen peroxide; a second enzyme uses that to "switch on the lamp", which is a chromogen, a color-making dye. The urine glucose line on your checkup report comes from this square.
Darker color,
more sugar
More sugar means more doors open, more lamps lit, and a deeper color. That's why the box has a color chart. Hold the strip up to it, and the closest match gives you a rough amount.
Hospitals often let a machine read the colors. Same idea, just more precise than the eye.
The square with no lock
A strip carries about ten squares, each with a different lock: one catches protein, one catches blood, one catches traces left by bacteria.
The pH square has no lock. Its dye changes color on its own: acidic is orange, and the more alkaline, the more it drifts to blue-green.
Pool and aquarium strips work the same way: every square hides one chemical, waiting for water.
Pregnancy tests look similar but work differently: they don't compare shades, they show whether an extra line appears.
Only a
quick first look
Quick check
Why does the sugar square change color only for sugar?
Glucose oxidase is the lock that only fits sugar: sugar goes in, the lock turns, and the chromogen lamp behind the door lights up.
