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Biochip

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A biochip is a highly engineered substrate that functions as a miniaturized laboratory.

Biochip
Biochip

These devices are designed to host a large number of simultaneous biochemical reactions on a single platform. By performing many tests at once, biochips allow scientists to efficiently screen large numbers of biological analytes. This capability is essential for modern medicine, ranging from rapid disease diagnosis to the detection of bioterrorism agents. Some advanced versions, known as digital microfluidic biochips, can manage fluid droplets dynamically. In these systems, adjacent cells in a microfluidic array can act as storage, perform functional operations, or transport droplets across the chip.

To function effectively, a biochip requires a complete analysis system beyond just the sensing component. The core of the system is the microarray, which is a dense, two-dimensional grid of biosensors.

Biochip
Biochip

These sensors are typically deposited on a flat substrate, such as glass or silicon. Some substrates are passive, while active substrates include integrated electronics or micromechanical devices to assist with signal transduction. Transduction is the critical process of translating a biological sensing event into a digital format. For example, a DNA binding event might be converted into a change in voltage, light intensity, or mass. A computer then processes this signal to produce a human-readable output.

There are several distinct types of biotechnology chips categorized by their specific biological targets. DNA microarrays are perhaps the most widely used, utilizing glass, silicon, or polymer supports to bind specific DNA sequences. Researchers use these to study gene expression, genetic variation, and gene function. Protein chips, or proteomics chips, are designed to detect and analyze proteins through immobilized proteins or antibodies. Another specialized type is the lab-on-a-chip (LOC) device. These integrate multiple laboratory functions, such as sample preparation, reaction, and analysis, into one compact platform. Finally, cell chips provide a specialized environment to grow and analyze living cells.

The history of biochip technology is built upon decades of foundational scientific discoveries. The journey began with early sensor technology, such as the glass pH electrode invented by Hughes in 1922. In 1953, Watson and Crick announced the discovery of the double helix structure of DNA, which revolutionized genetics research. By 1977, researchers Maxam and Gilbert, along with Sanger, developed techniques to sequence DNA. This allowed scientists to read the genetic codes used for protein synthesis. In 1983, Kary Mullis invented the polymerase chain reaction (PCR) to amplify DNA concentrations. This made it possible to detect extremely small quantities of DNA. Later, in 1986, Hood and his co-workers developed a method to label DNA with fluorescent tags, allowing these experiments to be observed optically.

Manufacturing a microarray presents significant technological and economic hurdles. One primary challenge is the precise placement of each unique sensor on a Cartesian grid. Many systems use robotic micro-pipetting or micro-printing to place tiny spots of sensor material on the surface. Because each sensor is unique, this serial process is low-throughput and expensive. To solve this, Fodor and colleagues developed a microlithography process to synthesize hundreds of thousands of unique DNA sensors. This method builds sensors one nucleotide at a time using light-directed steps. While powerful, this technique is currently limited to creating short DNA strands of 15 to 25 nucleotides.

An alternative manufacturing approach is known as random fabrication. Instead of using a strict coordinate system, sensors are placed at arbitrary positions on the chip. This allows for the use of parallelized self-assembly techniques, which are faster and cheaper. For example, Illumina used a design involving functionalized beads placed randomly in the wells of an etched fiber optic cable. In this scheme, each bead is uniquely encoded with a fluorescent signature. However, this method is limited by the number of unique dye combinations that can be successfully differentiated by the system.

Biochips offer incredible efficiency through a process called multiplexing. This refers to the ability to perform multiple analyses simultaneously within a single sample. In protein Biochip Array Technology, the chip replaces traditional tools like the ELISA plate. This allows a single sample to produce a complete patient profile for disease screening or monitoring treatment. For instance, the first commercial biochips, such as Affymetrix's GeneChip, contain thousands of individual DNA sensors. These can be used to sense defects, known as single nucleotide polymorphisms (SNPs), in specific genes like p53 or BRCA1 and BRCA2.

Biochip platform
Biochip platform

By reducing the required sample volume and processing time, biochips represent a massive leap in diagnostic capability.

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