Using nanoparticles to push the limits of detection

The size-dependent chemical and physical properties of nanoparticles inspire the design of unique assays and the use of new detection schemes while also offering the opportunity to vastly improve the results achieved when using traditional signal transduction methods. Herein, the most commonly exploited nanoparticle amplification schemes are organized and reviewed on the basis of the detection methods used to monitor the nanoparticle property of interest. The topics covered include the improved signal photostability and brightness of semiconductor quantum dots, the increased extinction coefficient of noble metal nanoparticles, the advantages of having a magnetic label on individual target molecules to facilitate separation, the multiplexing that is enabled with 'barcoded' nanoparticles, and the greatly amplified signals that can be achieved on the basis of conductivity changes, generated current, or simply by adding a 'massive' nanoparticle onto a small molecule target. Common approaches emerge among different nanoparticle materials and detection schemes, and it is also clear that there is still significant opportunity to use nanoparticles in as-yet-unimagined ways to further improve assay and sensor limits of detection.