Nano 來自希臘字，為 10 的冪次字首，奈米 (nanometer, 10–9m) 即為一公尺的十億分之一，約是人類頭髮直徑的百分之一，10 倍於氫原子直徑大小 (10–10m)，是一種長度單位，十億分之一公尺。當物質小到奈米尺寸時，將有別於塊材或分子狀態，會產生新特性，包括量子效應及表面效應等。這樣新特性的產生引發許多新的用途，當然新的問題也伴隨著產生。一般而言，小分子藥物進入身體後擴散至全身，雖然治療了病灶卻也帶給其他正常組織副作用。而利用奈米微粒當作藥物載體，可持續適量的釋放藥物，避免短時間內大量藥物攝入，造成強烈副作用。此外，奈米微粒藥物載體也可能躲避免疫系統，並有效地將藥物送入目標細胞，達成降低副作用的目的。但要設計這些新穎藥物傳遞模式，必須先通盤了解奈米微粒進入目標細胞的機制，才能有效治療病灶。隨著新穎奈米材料的應用越普及，人們暴露於這些奈米材料中將不自覺
地攝入體內，而這些奈米物質對人體的影響也需加以評估，以減少其帶來的傷害，這些安全評估須建立在奈米微粒進入組織細胞所產生的影響上。本文引用目前發表之相關科學報導，深入淺出地討論當生物基本構成單元的細胞遇到奈米微粒所發生的現象。

"Nano" may refer to the SI prefix representing 10–9. Nanometer stands for one billionth of a meter. The property of materials at nanoscale is markedly different from their counterparts at bulk levels due to the quantum effects. The development of nanotechnology emerges dynamically, and this technique has been applied widely, such as in nanomedicine. Once drug molecules enter the systemic circulation, they are generally distributed to the tissues,including normal and abnormal parts, leading to serious side effects. The application of nanomedicine, taking drug
delivery as an example, is able to significantly reduce non-specific drug accumulation and prolong drug release.
Additionally, drug encapsulated nanoparticles can be engineered to escape immune surveillance and to achieve higher targeting efficiency. In order to design nano-drugs with optimal performance, the understanding of the
processes operated by cells on uptaking and removal of these nanoparticles becomes vital. The properties of nanoparticles, such as size, shape, surface charges, and surface modification with ligands, are discussed herein to give a clear picture on how cell responses to these novel ultra-small particles.