Nanocrystalline cellulose (NCC) is a kind of rod-like nanomaterial obtained from inexpensive renewable biomass. The presence of hydroxyl groups on NCC surface allows it to be further functionalized through chemical modification or deposition of nanoparticles. An introduction of the assembly and deposition of metal element, non-metal element, metal oxide, non-metal oxide, and inorganic salt nanoparticles on NCC is presented in this review. NCC has important application value in many fields owing to the unique structure, exceptional strength and physicochemical properties, biocompatibility and low toxicity. NCC has been widely used as reinforcing agent because of its nanoscale dimensions and outstanding mechanical strength. As a nanoscale biotemplate suitable for the assembly of nanoparticles, NCC has been designed to be high-efficiency composite catalyst. With the characteristics of anisotropy, birefringence and liquid crystallinity, NCC has shown important applications as optical and electronic material. Since NCC is modifiable, biocompatible and biodegradable, this review espically focuses on the applications of NCC in the field of biomedicine, such as enzyme immobilization, antimicrobial and medical materials, biosensors, fluorescent probes and drug delivery. The practical considerations including stability, compatibility and cytotoxicity are also discussed. In the future, NCC still needs to overcome the problems of dispersity, intrinsic hydrophily and manufacturing difficulty to realize industrialization and commercialization.

Contents
1 Introduction
2 Functionalization of NCC
2.1 Covalent modification
2.2 Deposition of nanoparticles on NCC
3 Applications of NCC
3.1 Reinforced composites
3.2 Catalysis
3.3 Optical and electronic materials
3.4 Enzyme immobilization
3.5 Antimicrobial and medical materials
3.6 Biosensors
3.7 Fluorescent probes
3.8 Drug delivery
4 Outlook