The most unique and astounding property of quantum dots -- continuously tunable size dependent band gaps -- amazed and attracted numerous scientists over the past two decades or so. A spectrum of applications based on quantum dots have resulted. For instance, their bright colors due to fluorescent emission attract biologists to develop quantum dot based color markers and imaging agents; when electrically excited, they can produce richer colors than conventional approaches, which could enable next generation color displays; their natural ability of converting photons into electrons together with their solution-process compatibility makes them a promising candidate for affordable solar energy. The list goes on and on. Nevertheless, quantum dot researchers have always felt something significant is still missing. This is because the questions of how to best use the most unique property of quantum dots (continuously tunable size dependent band gaps) and what difference it can make have remained to be a puzzle. In this talk, I will introduce our recent work that changed this situation. I will show how we can take full advantage of this property to make highly miniaturized high performance spectrometers.