In fact, it may be the biggest obstacle of all. 而且，也许是最大的一个障碍。

How do we deploy this superweapon? 我们该如何部署这件超级武器？

I mean, every good weapon needs to be targeted, 每一件武器都要设定目标，

we have to target this superweapon to the supervillain cells that reside in the tumor. 我们要将这件超级武器瞄准潜伏在肿瘤内部的超级大反派。

But our bodies have a natural immune-defense system: 但人体是有免疫系统的：

cells that reside in the bloodstream and pick out things that don't belong, 血液里的各种细胞能辨认出外来物体，

so that it can destroy or eliminate them. 然后杀死或清除它们。

And guess what? Our nanoparticle is considered a foreign object. 很显然，我们的纳米粒子就是一种外来物体。

We have to sneak our nanoparticle past the tumor defense system. 我们要让它骗过肿瘤的防御系统。

We have to get it past this mechanism of getting rid of the foreign object by disguising it. 我们要伪装它，帮它通过重重岗哨，进入敌营。

So we add one more negatively charged layer around this nanoparticle, which serves two purposes. 于是我们再加上一层带负电的保护膜，包住我们的纳米粒子，目的有两个。

First, this outer layer is one of the naturally charged, highly hydrated polysaccharides that resides in our body. 第一，最外面这层保护膜是存在于我们体内的带电多糖水合物之一。

It creates a cloud of water molecules around the nanoparticle that gives us an invisibility cloaking effect. 它能在纳米粒子周围形成许多水分子，就像给纳米粒子穿上了隐形披风。

This invisibility cloak allows the nanoparticle 这件披风能帮助纳米粒子

to travel through the bloodstream long and far enough to reach the tumor, without getting eliminated by the body. 在血液里自由行动，畅通无阻，直到抵达肿瘤细胞。

Second, this layer contains molecules which bind specifically to our tumor cell. 第二，这层保护膜含有一些分子，专门用来与肿瘤细胞结合。

Once bound, the cancer cell takes up the nanoparticle, 一旦结合，癌细胞就会把纳米粒子吸收，

and now we have our nanoparticle inside the cancer cell and ready to deploy. 这样我们的纳米粒子最终就会进入癌细胞，准备发起进攻。

Alright! I feel the same way. Let's go! 是啊！我也觉得很兴奋。继续！