A new experimental paradigm, based on the detection of individual molecules, has been making great strides in the dissection of biomolecular function in vitro in the past two decades. A technological convergence – of improved detectors, probes, microfl uidics and other tools – is leading both to an explosion of this area of research and its development into a tool for investigating processes in living cells.
Imagine a busy motorway, packed with all kinds of vehicles. Now imagine that you are trying to describe the traffi c on that motorway (see Figure I.1 ). You could try to summarize it by a single number; the average speed of the traffi c would be a good example. This gives a good indication as to whether the traffi c is fl owing or obeying the speed limit, but it does not tell you much more. Sports cars may be tearing along in the outside lane, more cautious drivers cruising in the center lane, while trucks rumble along in the slow lane. Indeed, some vehicles may be pulled over on the hard shoulder. What’s more, vehicles will occasionally change lanes, slow down, or accelerate. We don’t get a full picture of this diversity from a single number, but this is the kind of measurement of molecular properties, quantities, or behavior that we usually make in the life sciences