**3.1 Graphdiyne**

Graphdiyne (GDY) is a new two-dimensional all-carbon allotrope composed of benzene rings and alkyne unites.

The carbon based nanomaterials are usually used to build electrochemical biosensors because of their physical and chemical properties. According to conventional carbon nanomaterials, GDY possesses richer carbon chemical bonds, which are of great importance for their practical applications. More importantly, GDY has a typical 2D structure similar to graphene, but also has the properties of threedimensional materials such as a hard carbon network and uniformly distributed pores that can greatly increase active bonding areas [19, 20].

**Figure 2** illustrates surface characterization of GDY [21].

As can be seen from this figure it is clear that GDY has a porous structure which is very important in sensor design to the effective diffusion of the analyte to the sensor surface.

**Figure 2.** *A) SEM, B) TEM and C) HRTEM of GDY.*

There are studies in which GDY has been used in the preparation of electrochemical enzyme biosensors [21], for microRNA testing [22] and in the determination of bacterium [23]. GDY was investigated as matrix for tyrosinase (a model enzyme) immobilization to create a mediator-free GDY based biosensor for rapid detection of bisphenol A (BPA). In this study between different carbon nanomaterial based biosensors including carbon nanotube and graphene was compared and it was reported, GDY-based tyrosinase biosensor performed better analytical for BPA detection than CNTs and graphene-based biosensors [21]. A new photoactive material has been synthesized that integrates the properties of MoS2 and GDY to implement ultra-sensitive detection of microRNA [22]. Controllable synthesis of two-dimensional graphite nanosheet (GDY NS) is of great importance for the clinical diagnosis and treatment of tuberculosis [23].

It is though that as a new promising 2D all-carbon nanomaterial after graphene, graphdiyne with intriguing properties would inevitably attract the general interest of scientists.
